apps: add http client

Signed-off-by: goldsimon <goldsimon@gmx.de>

src/apps/http/http_client.c

@@ -0,0 +1,838 @@
+/**
+ * @file
+ * HTTP client
+ */
+
+/*
+ * Copyright (c) 2018 Simon Goldschmidt <goldsimon@gmx.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ *
+ * Author: Simon Goldschmidt <goldsimon@gmx.de>
+ *
+ * @todo:
+ * - persistent connections
+ * - select outgoing http version
+ * - optionally follow redirect
+ * - check request uri for invalid characters? (e.g. encode spaces)
+ */
+
+#include "lwip/apps/http_client.h"
+
+#include "lwip/altcp_tcp.h"
+#include "lwip/dns.h"
+#include "lwip/debug.h"
+#include "lwip/mem.h"
+#include "lwip/altcp_tls.h"
+
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * HTTPC_DEBUG: Enable debugging for HTTP client.
+ */
+#ifndef HTTPC_DEBUG
+#define HTTPC_DEBUG                 LWIP_DBG_OFF
+#endif
+
+/** Set this to 1 to keep server name and uri in request state */
+#ifndef HTTPC_DEBUG_REQUEST
+#define HTTPC_DEBUG_REQUEST         0
+#endif
+
+/* the various debug levels for this file */
+#define HTTPC_DEBUG_TRACE        (HTTPC_DEBUG | LWIP_DBG_TRACE)
+#define HTTPC_DEBUG_STATE        (HTTPC_DEBUG | LWIP_DBG_STATE)
+#define HTTPC_DEBUG_WARN         (HTTPC_DEBUG | LWIP_DBG_LEVEL_WARNING)
+#define HTTPC_DEBUG_WARN_STATE   (HTTPC_DEBUG | LWIP_DBG_LEVEL_WARNING | LWIP_DBG_STATE)
+#define HTTPC_DEBUG_SERIOUS      (HTTPC_DEBUG | LWIP_DBG_LEVEL_SERIOUS)
+
+#define HTTPC_POLL_INTERVAL     1
+#define HTTPC_POLL_TIMEOUT      30 /* 15 seconds */
+
+#define HTTPC_CONTENT_LEN_INVALID 0xFFFFFFFF
+
+/* GET request basic */
+#define HTTPC_REQ_11 "GET %s HTTP/1.1\r\n" /* URI */\
+    "User-Agent: Wget/1.15 (linux-gnu)\r\n" \
+    "Accept: */*\r\n" \
+    "Connection: Close\r\n" /* we don't support persistent connections, yet */ \
+    "\r\n"
+#define HTTPC_REQ_11_FORMAT(uri) HTTPC_REQ_11, uri
+
+/* GET request with host */
+#define HTTPC_REQ_11_HOST "GET %s HTTP/1.1\r\n" /* URI */\
+    "User-Agent: Wget/1.15 (linux-gnu)\r\n" \
+    "Accept: */*\r\n" \
+    "Host: %s\r\n" /* server name */ \
+    "Connection: Close\r\n" /* we don't support persistent connections, yet */ \
+    "\r\n"
+#define HTTPC_REQ_11_HOST_FORMAT(uri, srv_name) HTTPC_REQ_11_HOST, uri, srv_name
+
+/* GET request with proxy: @todo */
+#define HTTPC_REQ_11_PROXY "GET %s%s HTTP/1.1\r\n" /* PROXY, URI */\
+    "User-Agent: Wget/1.15 (linux-gnu)\r\n" \
+    "Accept: */*\r\n" \
+    "Host: %s\r\n" /* server name */ \
+    "Connection: Close\r\n" /* we don't support persistent connections, yet */ \
+    "\r\n"
+#define HTTPC_REQ_11_PROXY_FORMAT(proxy, uri, srv_name) HTTPC_REQ_11_PROXY, proxy, uri, srv_name
+
+typedef enum ehttpc_parse_state {
+  HTTPC_PARSE_WAIT_FIRST_LINE = 0,
+  HTTPC_PARSE_WAIT_HEADERS,
+  HTTPC_PARSE_RX_DATA
+} httpc_parse_state_t;
+
+typedef struct _httpc_state
+{
+  struct altcp_pcb* pcb;
+  ip_addr_t remote_addr;
+  u16_t remote_port;
+  int timeout_ticks;
+  struct pbuf *request;
+  struct pbuf *rx_hdrs;
+  u16_t rx_http_version;
+  u16_t rx_status;
+  altcp_recv_fn recv_fn;
+  const httpc_connection_t *conn_settings;
+  void* callback_arg;
+  u32_t rx_content_len;
+  u32_t hdr_content_len;
+  httpc_parse_state_t parse_state;
+#if HTTPC_DEBUG_REQUEST
+  char* server_name;
+  char* uri;
+#endif
+} httpc_state_t;
+
+/** Free http client state and deallocate all resources within */
+static err_t
+httpc_free_state(httpc_state_t* req)
+{
+  struct altcp_pcb* tpcb;
+
+  if (req->request != NULL) {
+    pbuf_free(req->request);
+    req->request = NULL;
+  }
+  if (req->rx_hdrs != NULL) {
+    pbuf_free(req->rx_hdrs);
+    req->rx_hdrs = NULL;
+  }
+
+  tpcb = req->pcb;
+  mem_free(req);
+  req = NULL;
+
+  if (tpcb != NULL) {
+    err_t r;
+    altcp_arg(tpcb, NULL);
+    altcp_recv(tpcb, NULL);
+    altcp_err(tpcb, NULL);
+    altcp_poll(tpcb, NULL, 0);
+    altcp_sent(tpcb, NULL);
+    r = altcp_close(tpcb);
+    if (r != ERR_OK) {
+      altcp_abort(tpcb);
+      return ERR_ABRT;
+    }
+  }
+  return ERR_OK;
+}
+
+/** Close the connection: call finished callback and free the state */
+static err_t
+httpc_close(httpc_state_t* req, httpc_result_t result, u32_t server_response, err_t err)
+{
+  if (req != NULL) {
+    if (req->conn_settings != NULL) {
+      if (req->conn_settings->result_fn != NULL) {
+        req->conn_settings->result_fn(req->callback_arg, result, req->rx_content_len, server_response, err);
+      }
+    }
+    return httpc_free_state(req);
+  }
+  return ERR_OK;
+}
+
+/** Parse http header response line 1 */
+static err_t
+http_parse_response_status(struct pbuf *p, u16_t *http_version, u16_t *http_status, u16_t *http_status_str_offset)
+{
+  u16_t end1 = pbuf_memfind(p, "\r\n", 2, 0);
+  if (end1 != 0xFFFF) {
+    /* get parts of first line */
+    u16_t space1, space2;
+    space1 = pbuf_memfind(p, " ", 1, 0);
+    if (space1 != 0xFFFF) {
+      if ((pbuf_memcmp(p, 0, "HTTP/", 5) == 0)  && (pbuf_get_at(p, 6) == '.')) {
+        char status_num[10];
+        size_t status_num_len;
+        /* parse http version */
+        u16_t version = pbuf_get_at(p, 5) - '0';
+        version <<= 8;
+        version |= pbuf_get_at(p, 7) - '0';
+        *http_version = version;
+
+        /* parse http status number */
+        space2 = pbuf_memfind(p, " ", 1, space1 + 1);
+        if (space2 != 0xFFFF) {
+          *http_status_str_offset = space2 + 1;
+          status_num_len = space2 - space1 - 1;
+        } else {
+          status_num_len = end1 - space1 - 1;
+        }
+        memset(status_num, 0, sizeof(status_num));
+        if (pbuf_copy_partial(p, status_num, (u16_t)status_num_len, space1 + 1) == status_num_len) {
+          int status = atoi(status_num);
+          if ((status > 0) && (status <= 0xFFFF)) {
+            *http_status = (u16_t)status;
+            return ERR_OK;
+          }
+        }
+      }
+    }
+  }
+  return ERR_VAL;
+}
+
+/** Wait for all headers to be received, return its length and content-length (if available) */
+static err_t
+http_wait_headers(struct pbuf *p, u32_t *content_length, u16_t *total_header_len)
+{
+  u16_t end1 = pbuf_memfind(p, "\r\n\r\n", 4, 0);
+  if (end1 < (0xFFFF - 2)) {
+    /* all headers received */
+    /* check if we have a content length (@todo: case insensitive?) */
+    u16_t content_len_hdr;
+    *content_length = HTTPC_CONTENT_LEN_INVALID;
+    *total_header_len = end1 + 4;
+
+    content_len_hdr = pbuf_memfind(p, "Content-Length: ", 16, 0);
+    if (content_len_hdr != 0xFFFF) {
+      u16_t content_len_line_end = pbuf_memfind(p, "\r\n", 2, content_len_hdr);
+      if (content_len_line_end != 0xFFFF) {
+        char content_len_num[16];
+        u16_t content_len_num_len = (u16_t)(content_len_line_end - content_len_hdr - 16);
+        memset(content_len_num, 0, sizeof(content_len_num));
+        if (pbuf_copy_partial(p, content_len_num, content_len_num_len, content_len_hdr + 16) == content_len_num_len) {
+          int len = atoi(content_len_num);
+          if ((len >= 0) && (len < HTTPC_CONTENT_LEN_INVALID)) {
+            *content_length = (u32_t)len;
+          }
+        }
+      }
+    }
+    return ERR_OK;
+  }
+  return ERR_VAL;
+}
+
+/** http client tcp recv callback */
+static err_t
+httpc_tcp_recv(void *arg, struct altcp_pcb *pcb, struct pbuf *p, err_t r)
+{
+  err_t ret = ERR_OK;
+  httpc_state_t* req = (httpc_state_t*)arg;
+  LWIP_UNUSED_ARG(r);
+
+  if (p == NULL) {
+    return httpc_close(req, HTTPC_RESULT_OK, req->rx_status, ERR_OK);
+  }
+  if (req->parse_state != HTTPC_PARSE_RX_DATA) {
+    if (req->rx_hdrs == NULL) {
+      req->rx_hdrs = p;
+    } else {
+      pbuf_cat(req->rx_hdrs, p);
+    }
+    if (req->parse_state == HTTPC_PARSE_WAIT_FIRST_LINE) {
+      u16_t status_str_off;
+      err_t err = http_parse_response_status(req->rx_hdrs, &req->rx_http_version, &req->rx_status, &status_str_off);
+      if (err == ERR_OK) {
+        /* don't care status string */
+        req->parse_state = HTTPC_PARSE_WAIT_HEADERS;
+      }
+    }
+    if (req->parse_state == HTTPC_PARSE_WAIT_HEADERS) {
+      u16_t total_header_len;
+      err_t err = http_wait_headers(p, &req->hdr_content_len, &total_header_len);
+      if (err == ERR_OK) {
+        /* hide header bytes in pbuf */
+        struct pbuf *q;
+        if (req->conn_settings) {
+          if (req->conn_settings->headers_done_fn) {
+            err = req->conn_settings->headers_done_fn(req, req->callback_arg, req->rx_hdrs, total_header_len, req->hdr_content_len);
+            if (err != ERR_OK) {
+              return httpc_close(req, HTTPC_RESULT_LOCAL_ABORT, req->rx_status, err);
+            }
+          }
+        }
+        q = pbuf_free_header(req->rx_hdrs, total_header_len);
+        p = q;
+        req->rx_hdrs = NULL;
+        /* go on with data */
+        req->parse_state = HTTPC_PARSE_RX_DATA;
+      }
+    }
+  }
+  if ((p != NULL) && (req->parse_state == HTTPC_PARSE_RX_DATA)) {
+    req->rx_content_len += p->tot_len;
+    if (req->recv_fn != NULL) {
+      ret = req->recv_fn(req->callback_arg, pcb, p, r);
+    } else {
+      altcp_recved(pcb, p->tot_len);
+      pbuf_free(p);
+    }
+  }
+  return ERR_OK;
+}
+
+/** http client tcp err callback */
+static void
+httpc_tcp_err(void *arg, err_t err)
+{
+  httpc_state_t* req = (httpc_state_t*)arg;
+  if (req != NULL) {
+    /* pcb has already been deallocated */
+    req->pcb = NULL;
+    httpc_close(req, HTTPC_RESULT_ERR_CLOSED, 0, err);
+  }
+}
+
+/** http client tcp poll callback */
+static err_t
+httpc_tcp_poll(void *arg, struct altcp_pcb *pcb)
+{
+  /* implement timeout */
+  httpc_state_t* req = (httpc_state_t*)arg;
+  LWIP_UNUSED_ARG(pcb);
+  if (req != NULL) {
+    if (req->timeout_ticks) {
+      req->timeout_ticks--;
+    }
+    if (!req->timeout_ticks) {
+      return httpc_close(req, HTTPC_RESULT_ERR_TIMEOUT, 0, ERR_OK);
+    }
+  }
+  return ERR_OK;
+}
+
+/** http client tcp sent callback */
+static err_t
+httpc_tcp_sent(void *arg, struct altcp_pcb *pcb, u16_t len)
+{
+  /* nothing to do here for now */
+  LWIP_UNUSED_ARG(arg);
+  LWIP_UNUSED_ARG(pcb);
+  LWIP_UNUSED_ARG(len);
+  return ERR_OK;
+}
+
+/** http client tcp connected callback */
+static err_t
+httpc_tcp_connected(void *arg, struct altcp_pcb *pcb, err_t err)
+{
+  err_t r;
+  httpc_state_t* req = (httpc_state_t*)arg;
+  LWIP_UNUSED_ARG(pcb);
+  LWIP_UNUSED_ARG(err);
+
+  /* send request; last char is zero termination */
+  r = altcp_write(req->pcb, req->request->payload, req->request->len - 1, TCP_WRITE_FLAG_COPY);
+  if (r != ERR_OK) {
+     /* could not write the single small request -> fail, don't retry */
+     return httpc_close(req, HTTPC_RESULT_ERR_MEM, 0, r);
+  }
+  /* everything written, we can free the request */
+  pbuf_free(req->request);
+  req->request = NULL;
+
+  altcp_output(req->pcb);
+  return ERR_OK;
+}
+
+/** Start the http request when the server IP addr is known */
+static err_t
+httpc_get_internal_addr(httpc_state_t* req, const ip_addr_t *ipaddr)
+{
+  err_t err;
+  LWIP_ASSERT("req != NULL", req != NULL);
+
+  if (&req->remote_addr != ipaddr) {
+    /* fill in remote addr if called externally */
+    req->remote_addr = *ipaddr;
+  }
+
+  err = altcp_connect(req->pcb, &req->remote_addr, req->remote_port, httpc_tcp_connected);
+  if (err == ERR_OK) {
+    return ERR_OK;
+  }
+  LWIP_DEBUGF(HTTPC_DEBUG_WARN_STATE, ("tcp_connect failed: %d\n", (int)err));
+  return err;
+}
+
+#if LWIP_IPV4 && LWIP_DNS
+/** DNS callback
+ * If ipaddr is non-NULL, resolving succeeded and the request can be sent, otherwise it failed.
+ */
+static void
+httpc_dns_found(const char* hostname, const ip_addr_t *ipaddr, void *arg)
+{
+  httpc_state_t* req = (httpc_state_t*)arg;
+  err_t err;
+  httpc_result_t result;
+
+  LWIP_UNUSED_ARG(hostname);
+
+  if (ipaddr != NULL) {
+    err = httpc_get_internal_addr(req, ipaddr);
+    if (err == ERR_OK) {
+      return;
+    }
+    result = HTTPC_RESULT_ERR_CONNECT;
+  } else {
+    LWIP_DEBUGF(HTTPC_DEBUG_WARN_STATE, ("httpc_dns_found: failed to resolve hostname: %s\n",
+      hostname));
+    result = HTTPC_RESULT_ERR_HOSTNAME;
+    err = ERR_ARG;
+  }
+  httpc_close(req, result, 0, err);
+}
+#endif /* LWIP_IPV4 && LWIP_DNS */
+
+/** Start the http request after converting 'server_name' to ip address (DNS or address string) */
+static err_t
+httpc_get_internal_dns(httpc_state_t* req, const char* server_name)
+{
+  err_t err;
+  LWIP_ASSERT("req != NULL", req != NULL);
+
+#if LWIP_DNS
+  err = dns_gethostbyname(server_name, &req->remote_addr, httpc_dns_found, req);
+#else
+  err = ipaddr_aton(server_name, &req->remote_addr) ? ERR_OK : ERR_ARG;
+#endif
+
+  if (err == ERR_OK) {
+    /* cached or IP-string */
+    err = httpc_get_internal_addr(req, &req->remote_addr);
+  } else if (err == ERR_INPROGRESS) {
+    return ERR_OK;
+  }
+  return err;
+}
+
+static int
+httpc_create_request_string(const httpc_connection_t *settings, const char* server_name, const char* uri,
+                            int use_host, char *buffer, size_t buffer_size)
+{
+  if (settings->use_proxy) {
+    LWIP_ASSERT("server_name != NULL", server_name != NULL);
+    return snprintf(buffer, buffer_size, HTTPC_REQ_11_PROXY_FORMAT(server_name, uri, server_name));
+  } else if (use_host) {
+    LWIP_ASSERT("server_name != NULL", server_name != NULL);
+    return snprintf(buffer, buffer_size, HTTPC_REQ_11_HOST_FORMAT(uri, server_name));
+  } else {
+    return snprintf(buffer, buffer_size, HTTPC_REQ_11_FORMAT(uri));
+  }
+}
+
+/** Initialize the connection struct */
+err_t
+httpc_init_connection_common(httpc_state_t **connection, const httpc_connection_t *settings, const char* server_name,
+                      u16_t server_port, const char* uri, altcp_recv_fn recv_fn, void* callback_arg, int use_host)
+{
+  size_t alloc_len;
+  mem_size_t mem_alloc_len;
+  int req_len, req_len2;
+  httpc_state_t *req;
+#if HTTPC_DEBUG_REQUEST
+  size_t server_name_len, uri_len;
+#endif
+
+  LWIP_ASSERT("uri != NULL", uri != NULL);
+
+  /* get request len */
+  req_len = httpc_create_request_string(settings, server_name, uri, use_host, NULL, 0);
+  if ((req_len < 0) || (req_len > 0xFFFF)) {
+    return ERR_VAL;
+  }
+  /* alloc state and request in one block */
+  alloc_len = sizeof(httpc_state_t);
+#if HTTPC_DEBUG_REQUEST
+  server_name_len = server_name ? strlen(server_name) : 0;
+  uri_len = strlen(uri);
+  alloc_len += server_name_len + 1 + uri_len + 1;
+#endif
+  mem_alloc_len = (mem_size_t)alloc_len;
+  if ((mem_alloc_len < alloc_len) || (req_len + 1 > 0xFFFF)) {
+    return ERR_VAL;
+  }
+
+  req = (httpc_state_t*)mem_malloc((mem_size_t)alloc_len);
+  if(req == NULL) {
+    return ERR_MEM;
+  }
+  memset(req, 0, sizeof(httpc_state_t));
+  req->timeout_ticks = HTTPC_POLL_TIMEOUT;
+  req->request = pbuf_alloc(PBUF_RAW, (u16_t)(req_len + 1), PBUF_RAM);
+  if (req->request == NULL) {
+    httpc_free_state(req);
+    return ERR_MEM;
+  }
+  if (req->request->next != NULL) {
+    /* need a pbuf in one piece */
+    httpc_free_state(req);
+    return ERR_MEM;
+  }
+  req->hdr_content_len = HTTPC_CONTENT_LEN_INVALID;
+#if HTTPC_DEBUG_REQUEST
+  req->server_name = (char*)(req + 1);
+  if (server_name) {
+    memcpy(req->server_name, server_name, server_name_len + 1);
+  }
+  req->uri = req->server_name + server_name_len + 1;
+  memcpy(req->uri, uri, uri_len + 1);
+#endif
+  req->pcb = altcp_tcp_new();
+  if(req->pcb == NULL) {
+    httpc_free_state(req);
+    return ERR_MEM;
+  }
+  req->remote_port = server_port;
+  altcp_arg(req->pcb, req);
+  altcp_recv(req->pcb, httpc_tcp_recv);
+  altcp_err(req->pcb, httpc_tcp_err);
+  altcp_poll(req->pcb, httpc_tcp_poll, HTTPC_POLL_INTERVAL);
+  altcp_sent(req->pcb, httpc_tcp_sent);
+
+  /* set up request buffer */
+  req_len2 = httpc_create_request_string(settings, server_name, uri, use_host,
+    (char *)req->request->payload, req_len + 1);
+  if (req_len2 != req_len) {
+    httpc_free_state(req);
+    return ERR_VAL;
+  }
+
+  req->recv_fn = recv_fn;
+  req->conn_settings = settings;
+  req->callback_arg = callback_arg;
+
+  *connection = req;
+  return ERR_OK;
+}
+
+/** Initialize the connection struct */
+err_t
+httpc_init_connection(httpc_state_t **connection, const httpc_connection_t *settings, const char* server_name,
+                      u16_t server_port, const char* uri, altcp_recv_fn recv_fn, void* callback_arg)
+{
+  return httpc_init_connection_common(connection, settings, server_name, server_port, uri, recv_fn, callback_arg, 1);
+}
+
+
+/** Initialize the connection struct (from IP address) */
+err_t
+httpc_init_connection_addr(httpc_state_t **connection, const httpc_connection_t *settings,
+                           const ip_addr_t* server_addr, u16_t server_port, const char* uri,
+                           altcp_recv_fn recv_fn, void* callback_arg)
+{
+  char *server_addr_str = ipaddr_ntoa(server_addr);
+  if (server_addr_str == NULL) {
+    return ERR_VAL;
+  }
+  return httpc_init_connection_common(connection, settings, server_addr_str, server_port, uri,
+    recv_fn, callback_arg, 1);
+}
+
+/** HTTP client API: get a file by passing server IP address
+ *
+ * @param server_addr IP address of the server to connect
+ * @param port tcp port of the server
+ * @param uri uri to get from the server, remember leading "/"!
+ * @param settings connection settings (callbacks, proxy, etc.)
+ * @param recv_fn the http body (not the headers) are passed to this callback
+ * @param callback_arg argument passed to all the callbacks
+ * @param connection retreives the connection handle (to match in callbacks)
+ * @return ERR_OK if starting the request succeeds (callback_fn will be called later)
+ *         or an error code
+ */
+err_t
+httpc_get_file(const ip_addr_t* server_addr, u16_t port, const char* uri, const httpc_connection_t *settings,
+               altcp_recv_fn recv_fn, void* callback_arg, httpc_state_t **connection)
+{
+  err_t err;
+  httpc_state_t* req;
+
+  LWIP_ERROR("invalid parameters", (server_addr != NULL) && (uri != NULL) && (recv_fn != NULL), return ERR_ARG;);
+
+  err = httpc_init_connection_addr(&req, settings, server_addr, port,
+    uri, recv_fn, callback_arg);
+  if (err != ERR_OK) {
+    return err;
+  }
+
+  err = httpc_get_internal_addr(req, server_addr);
+  if(err != ERR_OK) {
+    httpc_free_state(req);
+    return err;
+  }
+
+  if (connection != NULL) {
+    *connection = req;
+  }
+  return ERR_OK;
+}
+
+/** HTTP client API: get a file by passing server name as string (DNS name or IP address string)
+ *
+ * @param server_name server name as string (DNS name or IP address string)
+ * @param port tcp port of the server
+ * @param uri uri to get from the server, remember leading "/"!
+ * @param settings connection settings (callbacks, proxy, etc.)
+ * @param recv_fn the http body (not the headers) are passed to this callback
+ * @param callback_arg argument passed to all the callbacks
+ * @param connection retreives the connection handle (to match in callbacks)
+ * @return ERR_OK if starting the request succeeds (callback_fn will be called later)
+ *         or an error code
+ */
+err_t
+httpc_get_file_dns(const char* server_name, u16_t port, const char* uri, const httpc_connection_t *settings,
+                   altcp_recv_fn recv_fn, void* callback_arg, httpc_state_t **connection)
+{
+  err_t err;
+  httpc_state_t* req;
+
+  LWIP_ERROR("invalid parameters", (server_name != NULL) && (uri != NULL) && (recv_fn != NULL), return ERR_ARG;);
+
+  err = httpc_init_connection(&req, settings, server_name, port, uri, recv_fn, callback_arg);
+  if (err != ERR_OK) {
+    return err;
+  }
+
+  err = httpc_get_internal_dns(req, server_name);
+  if(err != ERR_OK) {
+    httpc_free_state(req);
+    return err;
+  }
+
+  if (connection != NULL) {
+    *connection = req;
+  }
+  return ERR_OK;
+}
+
+#if LWIP_HTTPC_HAVE_FILE_IO
+/* Implementation to disk via fopen/fwrite/fclose follows */
+
+typedef struct _httpc_filestate
+{
+  const char* local_file_name;
+  FILE *file;
+  httpc_connection_t settings;
+  const httpc_connection_t *client_settings;
+  void *callback_arg;
+} httpc_filestate_t;
+
+static void httpc_fs_result(void *arg, httpc_result_t httpc_result, u32_t rx_content_len,
+  u32_t srv_res, err_t err);
+
+/** Initalize http client state for download to file system */
+static err_t
+httpc_fs_init(httpc_filestate_t **filestate_out, const char* local_file_name,
+              const httpc_connection_t *settings, void* callback_arg)
+{
+  httpc_filestate_t *filestate;
+  size_t file_len, alloc_len;
+  FILE *f;
+
+  file_len = strlen(local_file_name);
+  alloc_len = sizeof(httpc_filestate_t) + file_len + 1;
+
+  filestate = (httpc_filestate_t *)mem_malloc(alloc_len);
+  if (filestate == NULL) {
+    return ERR_MEM;
+  }
+  memset(filestate, 0, sizeof(httpc_filestate_t));
+  filestate->local_file_name = (const char *)(filestate + 1);
+  memcpy((char *)(filestate + 1), local_file_name, file_len + 1);
+  filestate->file = NULL;
+  filestate->client_settings = settings;
+  filestate->callback_arg = callback_arg;
+  /* copy client settings but override result callback */
+  memcpy(&filestate->settings, settings, sizeof(httpc_connection_t));
+  filestate->settings.result_fn = httpc_fs_result;
+
+  f = fopen(local_file_name, "wb");
+  if(f == NULL) {
+    /* could not open file */
+    mem_free(filestate);
+    return ERR_VAL;
+  }
+  filestate->file = f;
+  *filestate_out = filestate;
+  return ERR_OK;
+}
+
+/** Free http client state for download to file system */
+static void
+httpc_fs_free(httpc_filestate_t *filestate)
+{
+  if (filestate != NULL) {
+    if (filestate->file != NULL) {
+      fclose(filestate->file);
+      filestate->file = NULL;
+    }
+    mem_free(filestate);
+  }
+}
+
+/** Connection closed (success or error) */
+static void
+httpc_fs_result(void *arg, httpc_result_t httpc_result, u32_t rx_content_len,
+                u32_t srv_res, err_t err)
+{
+  httpc_filestate_t *filestate = (httpc_filestate_t *)arg;
+  if (filestate != NULL) {
+    if (filestate->client_settings->result_fn != NULL) {
+      filestate->client_settings->result_fn(filestate->callback_arg, httpc_result, rx_content_len,
+        srv_res, err);
+    }
+    httpc_fs_free(filestate);
+  }
+}
+
+/** tcp recv callback */
+static err_t
+httpc_fs_tcp_recv(void *arg, struct altcp_pcb *pcb, struct pbuf *p, err_t err)
+{
+  httpc_filestate_t *filestate = (httpc_filestate_t*)arg;
+  struct pbuf* q;
+  LWIP_UNUSED_ARG(err);
+
+  LWIP_ASSERT("p != NULL", p != NULL);
+
+  for (q = p; q != NULL; q = q->next) {
+    fwrite(q->payload, 1, q->len, filestate->file);
+  }
+  altcp_recved(pcb, p->tot_len);
+  pbuf_free(p);
+  return ERR_OK;
+}
+
+/** HTTP client API: get a file to disk by passing server IP address
+ *
+ * @param server_addr IP address of the server to connect
+ * @param port tcp port of the server
+ * @param uri uri to get from the server, remember leading "/"!
+ * @param settings connection settings (callbacks, proxy, etc.)
+ * @param callback_arg argument passed to all the callbacks
+ * @param connection retreives the connection handle (to match in callbacks)
+ * @return ERR_OK if starting the request succeeds (callback_fn will be called later)
+ *         or an error code
+ */
+err_t
+httpc_get_file_to_disk(const ip_addr_t* server_addr, u16_t port, const char* uri, const httpc_connection_t *settings,
+                       void* callback_arg, const char* local_file_name, httpc_state_t **connection)
+{
+  err_t err;
+  httpc_state_t* req;
+  httpc_filestate_t *filestate;
+
+  LWIP_ERROR("invalid parameters", (server_addr != NULL) && (uri != NULL) && (local_file_name != NULL), return ERR_ARG;);
+
+  err = httpc_fs_init(&filestate, local_file_name, settings, callback_arg);
+  if (err != ERR_OK) {
+    return err;
+  }
+
+  err = httpc_init_connection_addr(&req, &filestate->settings, server_addr, port,
+    uri, httpc_fs_tcp_recv, filestate);
+  if (err != ERR_OK) {
+    httpc_fs_free(filestate);
+    return err;
+  }
+
+  err = httpc_get_internal_addr(req, server_addr);
+  if(err != ERR_OK) {
+    httpc_fs_free(filestate);
+    httpc_free_state(req);
+    return err;
+  }
+
+  if (connection != NULL) {
+    *connection = req;
+  }
+  return ERR_OK;
+}
+
+/** HTTP client API: get a file to disk by passing server name as string (DNS name or IP address string)
+ *
+ * @param server_name server name as string (DNS name or IP address string)
+ * @param port tcp port of the server
+ * @param uri uri to get from the server, remember leading "/"!
+ * @param settings connection settings (callbacks, proxy, etc.)
+ * @param callback_arg argument passed to all the callbacks
+ * @param connection retreives the connection handle (to match in callbacks)
+ * @return ERR_OK if starting the request succeeds (callback_fn will be called later)
+ *         or an error code
+ */
+err_t
+httpc_get_file_dns_to_disk(const char* server_name, u16_t port, const char* uri, const httpc_connection_t *settings,
+                           void* callback_arg, const char* local_file_name, httpc_state_t **connection)
+{
+  err_t err;
+  httpc_state_t* req;
+  httpc_filestate_t *filestate;
+
+  LWIP_ERROR("invalid parameters", (server_name != NULL) && (uri != NULL) && (local_file_name != NULL), return ERR_ARG;);
+
+  err = httpc_fs_init(&filestate, local_file_name, settings, callback_arg);
+  if (err != ERR_OK) {
+    return err;
+  }
+
+  err = httpc_init_connection(&req, &filestate->settings, server_name, port,
+    uri, httpc_fs_tcp_recv, filestate);
+  if (err != ERR_OK) {
+    httpc_fs_free(filestate);
+    return err;
+  }
+
+  err = httpc_get_internal_dns(req, server_name);
+  if(err != ERR_OK) {
+    httpc_fs_free(filestate);
+    httpc_free_state(req);
+    return err;
+  }
+
+  if (connection != NULL) {
+    *connection = req;
+  }
+  return ERR_OK;
+}
+#endif /* LWIP_HTTPC_HAVE_FILE_IO */

src/include/lwip/apps/http_client.h

@@ -0,0 +1,135 @@
+/**
+ * @file
+ * HTTP client
+ */
+
+/*
+ * Copyright (c) 2018 Simon Goldschmidt <goldsimon@gmx.de>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ *
+ * Author: Simon Goldschmidt <goldsimon@gmx.de>
+ *
+ */
+
+#ifndef LWIP_HDR_APPS_HTTP_CLIENT_H
+#define LWIP_HDR_APPS_HTTP_CLIENT_H
+
+#include "lwip/opt.h"
+#include "lwip/ip_addr.h"
+#include "lwip/err.h"
+#include "lwip/altcp.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** HTTPC_HAVE_FILE_IO: define this to 1 to have functions dowloading directly
+ * to disk via fopen/fwrite.
+ * These functions are example implementations of the interface only.
+ */
+#ifndef LWIP_HTTPC_HAVE_FILE_IO
+#define LWIP_HTTPC_HAVE_FILE_IO   0
+#endif
+
+/** The default TCP port used for HTTP */
+#define HTTP_DEFAULT_PORT         80
+
+typedef enum ehttpc_result {
+  /** File successfully received */
+  HTTPC_RESULT_OK            = 0,
+  /** Unknown error */
+  HTTPC_RESULT_ERR_UNKNOWN   = 1,
+  /** Connection to server failed */
+  HTTPC_RESULT_ERR_CONNECT   = 2,
+  /** Failed to resolve server hostname */
+  HTTPC_RESULT_ERR_HOSTNAME  = 3,
+  /** Connection unexpectedly closed by remote server */
+  HTTPC_RESULT_ERR_CLOSED    = 4,
+  /** Connection timed out (server didn't respond in time) */
+  HTTPC_RESULT_ERR_TIMEOUT   = 5,
+  /** Server responded with an error code */
+  HTTPC_RESULT_ERR_SVR_RESP  = 6,
+  /** Local memory error */
+  HTTPC_RESULT_ERR_MEM       = 7,
+  /** Local abort */
+  HTTPC_RESULT_LOCAL_ABORT   = 8
+} httpc_result_t;
+
+typedef struct _httpc_state httpc_state_t;
+
+/** Prototype of a http client callback function
+ *
+ * @param arg argument specified when initiating the request
+ * @param http_result result of the mail transfer (see enum httpc_result_t)
+ * @param rx_content_len number of bytes received (without headers)
+ * @param srv_res this contains the http status code received (if any)
+ * @param err an error returned by internal lwip functions, can help to specify
+ *            the source of the error but must not necessarily be != ERR_OK
+ */
+typedef void (*httpc_result_fn)(void *arg, httpc_result_t httpc_result, u32_t rx_content_len, u32_t srv_res, err_t err);
+
+/** Prototype of http client callback: called when the headers are received
+ *
+ * @param connection http client connection
+ * @param arg argument specified when initiating the request
+ * @param hdr header pbuf(s) (may contain data also)
+ * @param hdr_len length of the heders in 'hdr'
+ * @param content_len content length as received in the headers (-1 if not received)
+ * @return if != ERR_OK is returned, the connection is aborted
+ */
+typedef err_t (*httpc_headers_done_fn)(httpc_state_t *connection, void *arg, struct pbuf *hdr, u16_t hdr_len, u32_t content_len);
+
+typedef struct _httpc_connection {
+  ip_addr_t proxy_addr;
+  u16_t proxy_port;
+  u8_t use_proxy;
+  /* @todo: add username:pass? */
+
+  /* this callback is called when the transfer is finished (or aborted) */
+  httpc_result_fn result_fn;
+  /* this callback is called after receiving the http headers
+     It can abort the connection by returning != ERR_OK */
+  httpc_headers_done_fn headers_done_fn;
+} httpc_connection_t;
+
+err_t httpc_get_file(const ip_addr_t* server_addr, u16_t port, const char* uri, const httpc_connection_t *settings,
+                     altcp_recv_fn recv_fn, void* callback_arg, httpc_state_t **connection);
+err_t httpc_get_file_dns(const char* server_name, u16_t port, const char* uri, const httpc_connection_t *settings,
+                     altcp_recv_fn recv_fn, void* callback_arg, httpc_state_t **connection);
+
+#if LWIP_HTTPC_HAVE_FILE_IO
+err_t httpc_get_file_to_disk(const ip_addr_t* server_addr, u16_t port, const char* uri, const httpc_connection_t *settings,
+                     void* callback_arg, const char* local_file_name, httpc_state_t **connection);
+err_t httpc_get_file_dns_to_disk(const char* server_name, u16_t port, const char* uri, const httpc_connection_t *settings,
+                     void* callback_arg, const char* local_file_name, httpc_state_t **connection);
+#endif /* LWIP_HTTPC_HAVE_FILE_IO */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* LWIP_HDR_APPS_HTTP_CLIENT_H */