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fix: work around libcurl Brotli trailing-byte rejection (CURLE_WRITE_ERROR)

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Some CDNs (e.g. CloudFront/Brave Search) emit Brotli streams with 1+
trailing bytes after the logical end. The Brotli decoder succeeds, but
libcurl's brotli_do_write() (content_encoding.c:439) rejects unconsumed
input bytes as CURLE_WRITE_ERROR — even though all decompressed data was
delivered to the write callback.

Browsers accept such responses, so match that: when CURLE_WRITE_ERROR
arrives but our callback never errored and bytes were received, downgrade
to success.
This commit is contained in:
Pierre Tachoire
2026-06-22 15:25:12 +02:00
parent 5d62fdc0fc
commit 4a71e0a2ad
1 changed files with 26 additions and 5 deletions
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31
src/browser/HttpClient.zig
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@@ -1057,7 +1057,28 @@ fn isRedirectStatus(status: u16) bool {
fn processOneMessage(self: *Client, msg: http.Handles.MultiMessage, transfer: *Transfer) !bool {
// State at entry: .inflight = conn (multi just delivered a completion).
if (msg.err == null or msg.err.? == error.RecvError) {
// Workaround for libcurl Brotli trailing-byte rejection.
//
// Some CDNs (e.g. CloudFront serving Brave Search) emit a Brotli stream
// whose compressed payload has 1+ trailing bytes after the logical end.
// The Brotli decoder reports BROTLI_DECODER_RESULT_SUCCESS, but libcurl's
// brotli_do_write() (content_encoding.c:439) treats any unconsumed input
// bytes as CURLE_WRITE_ERROR. All decompressed body data has already been
// delivered to our write callback successfully.
//
// Browsers accept such responses (the decompressed content is valid), so
// we match that behavior: when CURLE_WRITE_ERROR arrives but our callback
// never errored and bytes were received, treat it as success.
const effective_err: ?anyerror = if (msg.err) |err| blk: {
if (err == error.WriteError and transfer.res.callback_error == null and transfer.res.bytes_received > 0) {
log.debug(.http, "WriteError downgraded", .{ .url = transfer.req.url, .bytes = transfer.res.bytes_received });
break :blk null;
}
break :blk err;
} else null;
if (effective_err == null or effective_err.? == error.RecvError) {
transfer.detectAuthChallenge(msg.conn);
}
@@ -1090,7 +1111,7 @@ fn processOneMessage(self: *Client, msg: http.Handles.MultiMessage, transfer: *T
// Handle redirects: reuse the same connection to preserve TCP state.
// A redirect status without a Location header is not a redirect, it's a
// final response and falls through so its body is delivered.
if (msg.err == null) {
if (effective_err == null) {
const status = try msg.conn.getResponseCode();
if (isRedirectStatus(status)) {
if (msg.conn.getResponseHeader("location", 0)) |location| {
@@ -1127,7 +1148,7 @@ fn processOneMessage(self: *Client, msg: http.Handles.MultiMessage, transfer: *T
// of the response per HTTP/1.1 when there is no Content-Length).
// We must check this before endTransfer, which may reset the easy handle.
const is_conn_close_recv = blk: {
const err = msg.err orelse break :blk false;
const err = effective_err orelse break :blk false;
if (err != error.RecvError) break :blk false;
const hdr = msg.conn.getResponseHeader("connection", 0) orelse break :blk true;
break :blk std.ascii.eqlIgnoreCase(hdr.value, "close");
@@ -1138,8 +1159,8 @@ fn processOneMessage(self: *Client, msg: http.Handles.MultiMessage, transfer: *T
// from .inflight; nothing to set here.)
transfer.state = .completing;
if (msg.err != null and !is_conn_close_recv) {
transfer.requestFailed(transfer.res.callback_error orelse msg.err.?, true);
if (effective_err != null and !is_conn_close_recv) {
transfer.requestFailed(transfer.res.callback_error orelse effective_err.?, true);
return true;
}