std.http.Server: handle expect: 100-continue requests

The API automatically handles these requests as expected. After
receiveHead(), the server has a chance to notice the expectation and do
something about it. If it does not, then the Server implementation will
handle it by sending the continuation header when the read stream is
created.

Both respond() and respondStreaming() send the continuation header as
part of discarding the request body, only if the read stream has not
already been created.

1 files changed, 69 insertions, 22 deletions

diff --git a/lib/std/http/Server.zig b/lib/std/http/Server.zig
index 4ce77a90c4..bc284f5517 100644
--- a/lib/std/http/Server.zig
+++ b/lib/std/http/Server.zig
@@ -313,11 +313,20 @@ pub const Request = struct {
 
         var first_buffer: [500]u8 = undefined;
         var h = std.ArrayListUnmanaged(u8).initBuffer(&first_buffer);
+        if (request.head.expect != null) {
+            // reader() and hence discardBody() above sets expect to null if it
+            // is handled. So the fact that it is not null here means unhandled.
+            h.appendSliceAssumeCapacity("HTTP/1.1 417 Expectation Failed\r\n");
+            if (keep_alive) h.appendSliceAssumeCapacity("connection: keep-alive\r\n");
+            h.appendSliceAssumeCapacity("content-length: 0\r\n\r\n");
+            try request.server.connection.stream.writeAll(h.items);
+            return;
+        }
         h.fixedWriter().print("{s} {d} {s}\r\n", .{
             @tagName(options.version), @intFromEnum(options.status), phrase,
         }) catch unreachable;
-        if (keep_alive)
-            h.appendSliceAssumeCapacity("connection: keep-alive\r\n");
+
+        if (keep_alive) h.appendSliceAssumeCapacity("connection: keep-alive\r\n");
 
         if (options.transfer_encoding) |transfer_encoding| switch (transfer_encoding) {
             .none => {},
@@ -452,25 +461,35 @@ pub const Request = struct {
 
         var h = std.ArrayListUnmanaged(u8).initBuffer(options.send_buffer);
 
-        h.fixedWriter().print("{s} {d} {s}\r\n", .{
-            @tagName(o.version), @intFromEnum(o.status), phrase,
-        }) catch unreachable;
-        if (keep_alive) h.appendSliceAssumeCapacity("connection: keep-alive\r\n");
+        const elide_body = if (request.head.expect != null) eb: {
+            // reader() and hence discardBody() above sets expect to null if it
+            // is handled. So the fact that it is not null here means unhandled.
+            h.appendSliceAssumeCapacity("HTTP/1.1 417 Expectation Failed\r\n");
+            if (keep_alive) h.appendSliceAssumeCapacity("connection: keep-alive\r\n");
+            h.appendSliceAssumeCapacity("content-length: 0\r\n\r\n");
+            break :eb true;
+        } else eb: {
+            h.fixedWriter().print("{s} {d} {s}\r\n", .{
+                @tagName(o.version), @intFromEnum(o.status), phrase,
+            }) catch unreachable;
+            if (keep_alive) h.appendSliceAssumeCapacity("connection: keep-alive\r\n");
+
+            if (options.content_length) |len| {
+                h.fixedWriter().print("content-length: {d}\r\n", .{len}) catch unreachable;
+            } else {
+                h.appendSliceAssumeCapacity("transfer-encoding: chunked\r\n");
+            }
 
-        if (options.content_length) |len| {
-            h.fixedWriter().print("content-length: {d}\r\n", .{len}) catch unreachable;
-        } else {
-            h.appendSliceAssumeCapacity("transfer-encoding: chunked\r\n");
-        }
+            for (o.extra_headers) |header| {
+                h.appendSliceAssumeCapacity(header.name);
+                h.appendSliceAssumeCapacity(": ");
+                h.appendSliceAssumeCapacity(header.value);
+                h.appendSliceAssumeCapacity("\r\n");
+            }
 
-        for (o.extra_headers) |header| {
-            h.appendSliceAssumeCapacity(header.name);
-            h.appendSliceAssumeCapacity(": ");
-            h.appendSliceAssumeCapacity(header.value);
             h.appendSliceAssumeCapacity("\r\n");
-        }
-
-        h.appendSliceAssumeCapacity("\r\n");
+            break :eb request.head.method == .HEAD;
+        };
 
         return .{
             .stream = request.server.connection.stream,
@@ -478,16 +497,20 @@ pub const Request = struct {
             .send_buffer_start = 0,
             .send_buffer_end = h.items.len,
             .content_length = options.content_length,
-            .elide_body = request.head.method == .HEAD,
+            .elide_body = elide_body,
             .chunk_len = 0,
         };
     }
 
-    pub const ReadError = net.Stream.ReadError || error{ HttpChunkInvalid, HttpHeadersOversize };
+    pub const ReadError = net.Stream.ReadError || error{
+        HttpChunkInvalid,
+        HttpHeadersOversize,
+    };
 
     fn read_cl(context: *const anyopaque, buffer: []u8) ReadError!usize {
         const request: *Request = @constCast(@alignCast(@ptrCast(context)));
         const s = request.server;
+
         const remaining_content_length = &request.reader_state.remaining_content_length;
         if (remaining_content_length.* == 0) {
             s.state = .ready;
@@ -515,6 +538,7 @@ pub const Request = struct {
     fn read_chunked(context: *const anyopaque, buffer: []u8) ReadError!usize {
         const request: *Request = @constCast(@alignCast(@ptrCast(context)));
         const s = request.server;
+
         const cp = &request.reader_state.chunk_parser;
         const head_end = request.head_end;
 
@@ -599,11 +623,33 @@ pub const Request = struct {
         return out_end;
     }
 
-    pub fn reader(request: *Request) std.io.AnyReader {
+    pub const ReaderError = Response.WriteError || error{
+        /// The client sent an expect HTTP header value other than
+        /// "100-continue".
+        HttpExpectationFailed,
+    };
+
+    /// In the case that the request contains "expect: 100-continue", this
+    /// function writes the continuation header, which means it can fail with a
+    /// write error. After sending the continuation header, it sets the
+    /// request's expect field to `null`.
+    ///
+    /// Asserts that this function is only called once.
+    pub fn reader(request: *Request) ReaderError!std.io.AnyReader {
         const s = request.server;
         assert(s.state == .received_head);
         s.state = .receiving_body;
         s.next_request_start = request.head_end;
+
+        if (request.head.expect) |expect| {
+            if (mem.eql(u8, expect, "100-continue")) {
+                try request.server.connection.stream.writeAll("HTTP/1.1 100 Continue\r\n\r\n");
+                request.head.expect = null;
+            } else {
+                return error.HttpExpectationFailed;
+            }
+        }
+
         switch (request.head.transfer_encoding) {
             .chunked => {
                 request.reader_state = .{ .chunk_parser = http.ChunkParser.init };
@@ -639,7 +685,8 @@ pub const Request = struct {
         const s = request.server;
         if (keep_alive and request.head.keep_alive) switch (s.state) {
             .received_head => {
-                _ = request.reader().discard() catch return false;
+                const r = request.reader() catch return false;
+                _ = r.discard() catch return false;
                 assert(s.state == .ready);
                 return true;
             },