diff --git a/lib/std/Build/Cache.zig b/lib/std/Build/Cache.zig
index 18988ab7fb..a58cdb91a3 100644
--- a/lib/std/Build/Cache.zig
+++ b/lib/std/Build/Cache.zig
@@ -335,7 +335,6 @@ pub const Manifest = struct {
         manifest_create: fs.File.OpenError,
         manifest_read: fs.File.ReadError,
         manifest_lock: fs.File.LockError,
-        manifest_seek: fs.File.SeekError,
         file_open: FileOp,
         file_stat: FileOp,
         file_read: FileOp,
@@ -609,12 +608,6 @@ pub const Manifest = struct {
                     var file = self.files.pop().?;
                     file.key.deinit(self.cache.gpa);
                 }
-                // Also, seek the file back to the start.
-                self.manifest_file.?.seekTo(0) catch |err| {
-                    self.diagnostic = .{ .manifest_seek = err };
-                    return error.CacheCheckFailed;
-                };
-
                 switch (try self.hitWithCurrentLock()) {
                     .hit => break :hit,
                     .miss => |m| break :digests m.file_digests_populated,
@@ -659,9 +652,8 @@ pub const Manifest = struct {
         return true;
     }
 
-    /// Assumes that `self.hash.hasher` has been updated only with the original digest, that
-    /// `self.files` contains only the original input files, and that `self.manifest_file.?` is
-    /// seeked to the start of the file.
+    /// Assumes that `self.hash.hasher` has been updated only with the original digest and that
+    /// `self.files` contains only the original input files.
     fn hitWithCurrentLock(self: *Manifest) HitError!union(enum) {
         hit,
         miss: struct {
@@ -670,12 +662,13 @@ pub const Manifest = struct {
     } {
         const gpa = self.cache.gpa;
         const input_file_count = self.files.entries.len;
-
-        const file_contents = self.manifest_file.?.reader().readAllAlloc(gpa, manifest_file_size_max) catch |err| switch (err) {
+        var manifest_reader = self.manifest_file.?.reader(); // Reads positionally from zero.
+        const limit: std.io.Reader.Limit = .limited(manifest_file_size_max);
+        const file_contents = manifest_reader.interface().readRemainingAlloc(gpa, limit) catch |err| switch (err) {
             error.OutOfMemory => return error.OutOfMemory,
             error.StreamTooLong => return error.OutOfMemory,
-            else => |e| {
-                self.diagnostic = .{ .manifest_read = e };
+            error.ReadFailed => {
+                self.diagnostic = .{ .manifest_read = manifest_reader.err.? };
                 return error.CacheCheckFailed;
             },
         };
diff --git a/lib/std/Build/Fuzz/WebServer.zig b/lib/std/Build/Fuzz/WebServer.zig
index d84c3ccd9c..620ab1ad71 100644
--- a/lib/std/Build/Fuzz/WebServer.zig
+++ b/lib/std/Build/Fuzz/WebServer.zig
@@ -109,7 +109,7 @@ fn accept(ws: *WebServer, connection: std.net.Server.Connection) void {
     var server: std.http.Server = .init(&br, &bw);
     var web_socket: std.http.WebSocket = undefined;
     var ws_recv_buffer: [0x4000]u8 align(4) = undefined;
-    while (server.state == .ready) {
+    while (server.reader.state == .ready) {
         var request = server.receiveHead() catch |err| switch (err) {
             error.HttpConnectionClosing => return,
             else => {
@@ -476,7 +476,7 @@ fn serveSourcesTar(ws: *WebServer, request: *std.http.Server.Request) !void {
     defer arena_instance.deinit();
     const arena = arena_instance.allocator();
 
-    var response = try request.respondStreaming(.{
+    var body_writer = try request.respondStreaming(.{
         .respond_options = .{
             .extra_headers = &.{
                 .{ .name = "content-type", .value = "application/x-tar" },
@@ -517,7 +517,7 @@ fn serveSourcesTar(ws: *WebServer, request: *std.http.Server.Request) !void {
 
     var cwd_cache: ?[]const u8 = null;
 
-    var response_writer = response.writer().unbuffered();
+    var response_writer = body_writer.interface().unbuffered();
     var archiver: std.tar.Writer = .{ .underlying_writer = &response_writer };
 
     for (deduped_paths) |joined_path| {
@@ -531,9 +531,7 @@ fn serveSourcesTar(ws: *WebServer, request: *std.http.Server.Request) !void {
         try archiver.writeFile(joined_path.sub_path, file, try file.stat());
     }
 
-    // intentionally omitting the pointless trailer
-    //try archiver.finish();
-    try response.end();
+    try body_writer.end();
 }
 
 fn memoizedCwd(arena: Allocator, opt_ptr: *?[]const u8) ![]const u8 {
diff --git a/lib/std/Build/Step.zig b/lib/std/Build/Step.zig
index a0066a6be2..01d01f626b 100644
--- a/lib/std/Build/Step.zig
+++ b/lib/std/Build/Step.zig
@@ -812,7 +812,7 @@ fn failWithCacheError(s: *Step, man: *const Build.Cache.Manifest, err: Build.Cac
     switch (err) {
         error.CacheCheckFailed => switch (man.diagnostic) {
             .none => unreachable,
-            .manifest_create, .manifest_read, .manifest_lock, .manifest_seek => |e| return s.fail("failed to check cache: {s} {s}", .{
+            .manifest_create, .manifest_read, .manifest_lock => |e| return s.fail("failed to check cache: {s} {s}", .{
                 @tagName(man.diagnostic), @errorName(e),
             }),
             .file_open, .file_stat, .file_read, .file_hash => |op| {
diff --git a/lib/std/http.zig b/lib/std/http.zig
index e808cd201e..1b507b4ee9 100644
--- a/lib/std/http.zig
+++ b/lib/std/http.zig
@@ -772,6 +772,7 @@ pub const BodyWriter = struct {
     /// * `endChunked`
     pub fn endUnflushed(w: *BodyWriter) WriteError!void {
         switch (w.state) {
+            .end => unreachable,
             .content_length => |len| {
                 assert(len == 0); // Trips when end() called before all bytes written.
                 w.state = .end;
@@ -1033,6 +1034,7 @@ pub const BodyWriter = struct {
                     .writeSplat = chunkedWriteSplat,
                     .writeFile = chunkedWriteFile,
                 },
+                .end => unreachable,
             },
         };
     }
diff --git a/lib/std/http/Server.zig b/lib/std/http/Server.zig
index e0c224c560..8efac3d0ef 100644
--- a/lib/std/http/Server.zig
+++ b/lib/std/http/Server.zig
@@ -11,7 +11,6 @@ const Server = @This();
 
 /// Data from the HTTP server to the HTTP client.
 out: *std.io.BufferedWriter,
-/// Internal state managed by this abstraction.
 reader: http.Reader,
 
 /// Initialize an HTTP server that can respond to multiple requests on the same
@@ -26,6 +25,7 @@ pub fn init(in: *std.io.BufferedReader, out: *std.io.BufferedWriter) Server {
         .reader = .{
             .in = in,
             .state = .ready,
+            .body_state = undefined,
         },
         .out = out,
     };
@@ -39,7 +39,7 @@ pub const ReceiveHeadError = http.Reader.HeadError || error{
     HttpHeadersInvalid,
 };
 
-pub fn receiveHead(s: *Server) http.Reader.HeadError!Request {
+pub fn receiveHead(s: *Server) ReceiveHeadError!Request {
     try s.reader.receiveHead();
     return .{
         .server = s,
@@ -490,13 +490,13 @@ pub const Request = struct {
 
         return .{
             .http_protocol_output = request.server.out,
-            .transfer_encoding = if (o.transfer_encoding) |te| switch (te) {
+            .state = if (o.transfer_encoding) |te| switch (te) {
                 .chunked => .{ .chunked = .init },
                 .none => .none,
             } else if (options.content_length) |len| .{
                 .content_length = len,
             } else .{ .chunked = .init },
-            .elide_body = elide_body,
+            .elide = elide_body,
         };
     }
 
diff --git a/lib/std/tar/Writer.zig b/lib/std/tar/Writer.zig
index 064168d21c..3b48fc17b2 100644
--- a/lib/std/tar/Writer.zig
+++ b/lib/std/tar/Writer.zig
@@ -50,9 +50,14 @@ pub fn writeFile(
     try w.setPath(&header, sub_path);
     try header.setSize(stat.size);
     try header.setMtime(mtime);
-    try header.write(w.underlying_writer);
+    try header.updateChecksum();
 
-    try w.underlying_writer.writeFileAll(file, .{ .limit = .limited(stat.size) });
+    var vec: [1][]const u8 = .{@ptrCast((&header)[0..1])};
+    try w.underlying_writer.writeFileAll(file, .{
+        .limit = .limited(stat.size),
+        .headers_and_trailers = &vec,
+        .headers_len = 1,
+    });
     try w.writePadding(stat.size);
 }