http: Implement trailing headers for chunked transfers

This adds the CURLOPT_TRAILERDATA and CURLOPT_TRAILERFUNCTION
options that allow a callback based approach to sending trailing headers
with chunked transfers.

The test server (sws) was updated to take into account the detection of the
end of transfer in the case of trailing headers presence.

Test 1591 checks that trailing headers can be sent using libcurl.

Closes #3350

5 files changed, 224 insertions, 21 deletions

diff --git a/lib/http.c b/lib/http.c
index 0a3e46243..07665743c 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -1681,6 +1681,52 @@ enum proxy_use {
   HEADER_CONNECT  /* sending CONNECT to a proxy */
 };
 
+/* used to compile the provided trailers into one buffer
+   will return an error code if one of the headers is
+   not formatted correctly */
+CURLcode Curl_http_compile_trailers(struct curl_slist *trailers,
+                                    Curl_send_buffer *buffer,
+                                    struct Curl_easy *handle)
+{
+  char *ptr = NULL;
+  CURLcode result = CURLE_OK;
+  const char *endofline_native = NULL;
+  const char *endofline_network = NULL;
+
+  /* TODO: Maybe split Curl_add_custom_headers to make it reusable here */
+
+  if(
+#ifdef CURL_DO_LINEEND_CONV
+     (handle->set.prefer_ascii) ||
+#endif
+     (handle->set.crlf)) {
+    /* \n will become \r\n later on */
+    endofline_native  = "\n";
+    endofline_network = "\x0a";
+  }
+  else {
+    endofline_native  = "\r\n";
+    endofline_network = "\x0d\x0a";
+  }
+
+  while(trailers) {
+    /* only add correctly formatted trailers */
+    ptr = strchr(trailers->data, ':');
+    if(ptr && *(ptr + 1) == ' ') {
+      result = Curl_add_bufferf(&buffer, "%s%s", trailers->data,
+                                endofline_native);
+      if(result)
+        return result;
+    }
+    else
+      infof(handle, "Malformatted trailing header ! Skipping trailer.");
+    trailers = trailers->next;
+  }
+  result = Curl_add_buffer(&buffer, endofline_network,
+                           strlen(endofline_network));
+  return result;
+}
+
 CURLcode Curl_add_custom_headers(struct connectdata *conn,
                                  bool is_connect,
                                  Curl_send_buffer *req_buffer)
diff --git a/lib/http.h b/lib/http.h
index 21fa701ab..7fa0471ad 100644
--- a/lib/http.h
+++ b/lib/http.h
@@ -74,6 +74,9 @@ CURLcode Curl_add_timecondition(struct Curl_easy *data,
 CURLcode Curl_add_custom_headers(struct connectdata *conn,
                                  bool is_connect,
                                  Curl_send_buffer *req_buffer);
+CURLcode Curl_http_compile_trailers(struct curl_slist *trailers,
+                                    Curl_send_buffer *buffer,
+                                    struct Curl_easy *handle);
 
 /* protocol-specific functions set up to be called by the main engine */
 CURLcode Curl_http(struct connectdata *conn, bool *done);
diff --git a/lib/setopt.c b/lib/setopt.c
index 01a890b39..27046768c 100644
--- a/lib/setopt.c
+++ b/lib/setopt.c
@@ -2636,6 +2636,16 @@ CURLcode Curl_vsetopt(struct Curl_easy *data, CURLoption option,
       return CURLE_BAD_FUNCTION_ARGUMENT;
     data->set.upkeep_interval_ms = arg;
     break;
+  case CURLOPT_TRAILERFUNCTION:
+#ifndef CURL_DISABLE_HTTP
+    data->set.trailer_callback = va_arg(param, curl_trailer_callback);
+#endif
+    break;
+  case CURLOPT_TRAILERDATA:
+#ifndef CURL_DISABLE_HTTP
+    data->set.trailer_data = va_arg(param, void *);
+#endif
+    break;
   default:
     /* unknown tag and its companion, just ignore: */
     result = CURLE_UNKNOWN_OPTION;
diff --git a/lib/transfer.c b/lib/transfer.c
index 6390821bb..7483cf1f8 100644
--- a/lib/transfer.c
+++ b/lib/transfer.c
@@ -117,6 +117,35 @@ CURLcode Curl_get_upload_buffer(struct Curl_easy *data)
   return CURLE_OK;
 }
 
+#ifndef CURL_DISABLE_HTTP
+/*
+ * This function will be called to loop through the trailers buffer
+ * until no more data is available for sending.
+ */
+static size_t Curl_trailers_read(char *buffer, size_t size, size_t nitems,
+                                 void *raw)
+{
+  struct Curl_easy *data = (struct Curl_easy *)raw;
+  Curl_send_buffer *trailers_buf = data->state.trailers_buf;
+  size_t bytes_left = trailers_buf->size_used-data->state.trailers_bytes_sent;
+  size_t to_copy = (size*nitems < bytes_left) ? size*nitems : bytes_left;
+  if(to_copy) {
+    memcpy(buffer,
+           &trailers_buf->buffer[data->state.trailers_bytes_sent],
+           to_copy);
+    data->state.trailers_bytes_sent += to_copy;
+  }
+  return to_copy;
+}
+
+static size_t Curl_trailers_left(void *raw)
+{
+  struct Curl_easy *data = (struct Curl_easy *)raw;
+  Curl_send_buffer *trailers_buf = data->state.trailers_buf;
+  return trailers_buf->size_used - data->state.trailers_bytes_sent;
+}
+#endif
+
 /*
  * This function will call the read callback to fill our buffer with data
  * to upload.
@@ -127,6 +156,17 @@ CURLcode Curl_fillreadbuffer(struct connectdata *conn, size_t bytes,
   struct Curl_easy *data = conn->data;
   size_t buffersize = bytes;
   size_t nread;
+
+#ifndef CURL_DISABLE_HTTP
+  struct curl_slist *trailers = NULL;
+  CURLcode c;
+  int trailers_ret_code;
+#endif
+
+  curl_read_callback readfunc = NULL;
+  void *extra_data = NULL;
+  bool added_crlf = FALSE;
+
 #ifdef CURL_DOES_CONVERSIONS
   bool sending_http_headers = FALSE;
 
@@ -140,15 +180,71 @@ CURLcode Curl_fillreadbuffer(struct connectdata *conn, size_t bytes,
   }
 #endif
 
-  if(data->req.upload_chunky) {
+#ifndef CURL_DISABLE_HTTP
+  if(data->state.trailers_state == TRAILERS_INITIALIZED) {
+    /* at this point we already verified that the callback exists
+       so we compile and store the trailers buffer, then proceed */
+    infof(data,
+          "Moving trailers state machine from initialized to sending.\n");
+    data->state.trailers_state = TRAILERS_SENDING;
+    data->state.trailers_buf = Curl_add_buffer_init();
+    if(!data->state.trailers_buf) {
+      failf(data, "Unable to allocate trailing headers buffer !");
+      return CURLE_OUT_OF_MEMORY;
+    }
+    data->state.trailers_bytes_sent = 0;
+    Curl_set_in_callback(data, true);
+    trailers_ret_code = data->set.trailer_callback(&trailers,
+                                                   data->set.trailer_data);
+    Curl_set_in_callback(data, false);
+    if(trailers_ret_code == CURL_TRAILERFUNC_OK) {
+      c = Curl_http_compile_trailers(trailers, data->state.trailers_buf, data);
+    }
+    else {
+      failf(data, "operation aborted by trailing headers callback");
+      *nreadp = 0;
+      c = CURLE_ABORTED_BY_CALLBACK;
+    }
+    if(c != CURLE_OK) {
+      Curl_add_buffer_free(&data->state.trailers_buf);
+      curl_slist_free_all(trailers);
+      return c;
+    }
+    infof(data, "Successfully compiled trailers.\r\n");
+    curl_slist_free_all(trailers);
+  }
+#endif
+
+  /* if we are transmitting trailing data, we don't need to write
+     a chunk size so we skip this */
+  if(data->req.upload_chunky &&
+     data->state.trailers_state == TRAILERS_NONE) {
     /* if chunked Transfer-Encoding */
     buffersize -= (8 + 2 + 2);   /* 32bit hex + CRLF + CRLF */
     data->req.upload_fromhere += (8 + 2); /* 32bit hex + CRLF */
   }
 
+#ifndef CURL_DISABLE_HTTP
+  if(data->state.trailers_state == TRAILERS_SENDING) {
+    /* if we're here then that means that we already sent the last empty chunk
+       but we didn't send a final CR LF, so we sent 0 CR LF. We then start
+       pulling trailing data until we ²have no more at which point we
+       simply return to the previous point in the state machine as if
+       nothing happened.
+       */
+    readfunc = Curl_trailers_read;
+    extra_data = (void *)data;
+  }
+  else
+#endif
+  {
+    readfunc = data->state.fread_func;
+    extra_data = data->state.in;
+  }
+
   Curl_set_in_callback(data, true);
-  nread = data->state.fread_func(data->req.upload_fromhere, 1,
-                                 buffersize, data->state.in);
+  nread = readfunc(data->req.upload_fromhere, 1,
+                   buffersize, extra_data);
   Curl_set_in_callback(data, false);
 
   if(nread == CURL_READFUNC_ABORT) {
@@ -203,7 +299,7 @@ CURLcode Curl_fillreadbuffer(struct connectdata *conn, size_t bytes,
     char hexbuffer[11];
     const char *endofline_native;
     const char *endofline_network;
-    int hexlen;
+    int hexlen = 0;
 
     if(
 #ifdef CURL_DO_LINEEND_CONV
@@ -218,20 +314,36 @@ CURLcode Curl_fillreadbuffer(struct connectdata *conn, size_t bytes,
       endofline_native  = "\r\n";
       endofline_network = "\x0d\x0a";
     }
-    hexlen = msnprintf(hexbuffer, sizeof(hexbuffer),
-                       "%x%s", nread, endofline_native);
 
-    /* move buffer pointer */
-    data->req.upload_fromhere -= hexlen;
-    nread += hexlen;
+    /* if we're not handling trailing data, proceed as usual */
+    if(data->state.trailers_state != TRAILERS_SENDING) {
+      hexlen = msnprintf(hexbuffer, sizeof(hexbuffer),
+                         "%x%s", nread, endofline_native);
 
-    /* copy the prefix to the buffer, leaving out the NUL */
-    memcpy(data->req.upload_fromhere, hexbuffer, hexlen);
+      /* move buffer pointer */
+      data->req.upload_fromhere -= hexlen;
+      nread += hexlen;
 
-    /* always append ASCII CRLF to the data */
-    memcpy(data->req.upload_fromhere + nread,
-           endofline_network,
-           strlen(endofline_network));
+      /* copy the prefix to the buffer, leaving out the NUL */
+      memcpy(data->req.upload_fromhere, hexbuffer, hexlen);
+
+      /* always append ASCII CRLF to the data unless
+         we have a valid trailer callback */
+#ifndef CURL_DISABLE_HTTP
+      if((nread-hexlen) == 0 &&
+          data->set.trailer_callback != NULL &&
+          data->state.trailers_state == TRAILERS_NONE) {
+        data->state.trailers_state = TRAILERS_INITIALIZED;
+      }
+      else
+#endif
+      {
+        memcpy(data->req.upload_fromhere + nread,
+               endofline_network,
+               strlen(endofline_network));
+        added_crlf = TRUE;
+      }
+    }
 
 #ifdef CURL_DOES_CONVERSIONS
     {
@@ -251,13 +363,29 @@ CURLcode Curl_fillreadbuffer(struct connectdata *conn, size_t bytes,
     }
 #endif /* CURL_DOES_CONVERSIONS */
 
-    if((nread - hexlen) == 0) {
-      /* mark this as done once this chunk is transferred */
+#ifndef CURL_DISABLE_HTTP
+    if(data->state.trailers_state == TRAILERS_SENDING &&
+       !Curl_trailers_left(data)) {
+      Curl_add_buffer_free(&data->state.trailers_buf);
+      data->state.trailers_state = TRAILERS_DONE;
+      data->set.trailer_data = NULL;
+      data->set.trailer_callback = NULL;
+      /* mark the transfer as done */
       data->req.upload_done = TRUE;
-      infof(data, "Signaling end of chunked upload via terminating chunk.\n");
+      infof(data, "Signaling end of chunked upload after trailers.\n");
     }
+    else
+#endif
+      if((nread - hexlen) == 0 &&
+         data->state.trailers_state != TRAILERS_INITIALIZED) {
+        /* mark this as done once this chunk is transferred */
+        data->req.upload_done = TRUE;
+        infof(data,
+              "Signaling end of chunked upload via terminating chunk.\n");
+      }
 
-    nread += strlen(endofline_native); /* for the added end of line */
+    if(added_crlf)
+      nread += strlen(endofline_network); /* for the added end of line */
   }
 #ifdef CURL_DOES_CONVERSIONS
   else if((data->set.prefer_ascii) && (!sending_http_headers)) {
@@ -925,7 +1053,6 @@ static CURLcode readwrite_upload(struct Curl_easy *data,
   *didwhat |= KEEP_SEND;
 
   do {
-
     /* only read more data if there's no upload data already
        present in the upload buffer */
     if(0 == k->upload_present) {
@@ -950,7 +1077,6 @@ static CURLcode readwrite_upload(struct Curl_easy *data,
           k->keepon &= ~KEEP_SEND;         /* disable writing */
           k->start100 = Curl_now();       /* timeout count starts now */
           *didwhat &= ~KEEP_SEND;  /* we didn't write anything actually */
-
           /* set a timeout for the multi interface */
           Curl_expire(data, data->set.expect_100_timeout, EXPIRE_100_TIMEOUT);
           break;
diff --git a/lib/urldata.h b/lib/urldata.h
index 448437d2a..8fb2d2894 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -1216,6 +1216,15 @@ typedef enum {
   EXPIRE_LAST /* not an actual timer, used as a marker only */
 } expire_id;
 
+
+typedef enum {
+  TRAILERS_NONE,
+  TRAILERS_INITIALIZED,
+  TRAILERS_SENDING,
+  TRAILERS_DONE
+} trailers_state;
+
+
 /*
  * One instance for each timeout an easy handle can set.
  */
@@ -1362,6 +1371,13 @@ struct UrlState {
 #endif
   CURLU *uh; /* URL handle for the current parsed URL */
   struct urlpieces up;
+#ifndef CURL_DISABLE_HTTP
+  size_t trailers_bytes_sent;
+  Curl_send_buffer *trailers_buf; /* a buffer containing the compiled trailing
+                                  headers */
+#endif
+  trailers_state trailers_state; /* whether we are sending trailers
+                                       and what stage are we at */
 };
 
 
@@ -1730,6 +1746,8 @@ struct UserDefined {
   multidone_func fmultidone;
   struct Curl_easy *dohfor; /* this is a DoH request for that transfer */
   CURLU *uh; /* URL handle for the current parsed URL */
+  void *trailer_data; /* pointer to pass to trailer data callback */
+  curl_trailer_callback trailer_callback; /* trailing data callback */
 };
 
 struct Names {