[bun dev] Implement `hash:` namespace for `file` loader to improve browser cache invalidation

This appends a hash to URLs and import paths

In `bun dev`, this means:
  `/foo.woff2` => `/hash:/foo.woff2`

`bun dev` simply ignores this.

3 files changed, 70 insertions, 22 deletions

diff --git a/src/fs.zig b/src/fs.zig
index f11651ae7..7218f7987 100644
--- a/src/fs.zig
+++ b/src/fs.zig
@@ -662,14 +662,26 @@ pub const FileSystem = struct {
             mtime: i128 = 0,
             mode: std.fs.File.Mode = 0,
 
-            threadlocal var hash_bytes: [32]u8 = undefined;
             threadlocal var hash_name_buf: [1024]u8 = undefined;
 
             pub fn hashName(
                 this: *const ModKey,
                 basename: string,
             ) !string {
+                return try std.fmt.bufPrint(
+                    &hash_name_buf,
+                    "{s}-{x}",
+                    .{
+                        basename,
+                        this.hash(),
+                    },
+                );
+            }
 
+            pub fn hash(
+                this: *const ModKey,
+            ) u64 {
+                var hash_bytes: [32]u8 = undefined;
                 // We shouldn't just read the contents of the ModKey into memory
                 // The hash should be deterministic across computers and operating systems.
                 // inode is non-deterministic across volumes within the same compuiter
@@ -679,15 +691,10 @@ pub const FileSystem = struct {
                 std.mem.writeIntNative(@TypeOf(this.size), hash_bytes_remain[0..@sizeOf(@TypeOf(this.size))], this.size);
                 hash_bytes_remain = hash_bytes_remain[@sizeOf(@TypeOf(this.size))..];
                 std.mem.writeIntNative(@TypeOf(this.mtime), hash_bytes_remain[0..@sizeOf(@TypeOf(this.mtime))], this.mtime);
-
-                return try std.fmt.bufPrint(
-                    &hash_name_buf,
-                    "{s}-{x}",
-                    .{
-                        basename,
-                        @truncate(u32, std.hash.Wyhash.hash(1, &hash_bytes)),
-                    },
-                );
+                hash_bytes_remain = hash_bytes_remain[@sizeOf(@TypeOf(this.mtime))..];
+                std.debug.assert(hash_bytes_remain.len == 8);
+                hash_bytes_remain[0..8].* = @bitCast([8]u8, @as(u64, 0));
+                return std.hash.Wyhash.hash(0, &hash_bytes);
             }
 
             pub fn generate(_: *RealFS, _: string, file: std.fs.File) anyerror!ModKey {
diff --git a/src/http.zig b/src/http.zig
index 62a07cfc0..89ed1fe97 100644
--- a/src/http.zig
+++ b/src/http.zig
@@ -2636,9 +2636,26 @@ pub const RequestContext = struct {
             return true;
         }
 
-        if (ctx.url.path.len > "blob:".len and strings.eqlComptimeIgnoreLen(ctx.url.path[0.."blob:".len], "blob:")) {
-            try ctx.handleBlobURL(server);
-            return true;
+        if (ctx.url.path.len > "blob:".len) {
+            if (strings.eqlComptimeIgnoreLen(ctx.url.path[0.."blob:".len], "blob:")) {
+                try ctx.handleBlobURL(server);
+                return true;
+            }
+
+            // From HTTP, we serve files with a hash modkey
+            // The format is
+            //    hash:${hash}/${ORIGINAL_PATH}
+            //    hash:abcdefg123/app/foo/my-file.jpeg
+            // The hash exists for browser cache invalidation
+            if (strings.eqlComptimeIgnoreLen(ctx.url.path[0.."hash:".len], "hash:")) {
+                var current = ctx.url.path;
+                current = current["hash:".len..];
+                if (strings.indexOfChar(current, '/')) |i| {
+                    current = current[i + 1 ..];
+                    ctx.url.path = current;
+                    return false;
+                }
+            }
         }
 
         const isMaybePrefix = ctx.url.path.len > "bun:".len;
diff --git a/src/linker.zig b/src/linker.zig
index b108ccce7..1ddcc1eef 100644
--- a/src/linker.zig
+++ b/src/linker.zig
@@ -92,6 +92,20 @@ pub const Linker = struct {
         };
     }
 
+    pub fn getModKey(
+        this: *ThisLinker,
+        file_path: Fs.Path,
+        fd: ?FileDescriptorType,
+    ) !Fs.FileSystem.RealFS.ModKey {
+        var file: std.fs.File = if (fd) |_fd| std.fs.File{ .handle = _fd } else try std.fs.openFileAbsolute(file_path.text, .{ .read = true });
+        Fs.FileSystem.setMaxFd(file.handle);
+        const modkey = try Fs.FileSystem.RealFS.ModKey.generate(&this.fs.fs, file_path.text, file);
+
+        if (fd == null)
+            file.close();
+        return modkey;
+    }
+
     pub fn getHashedFilename(
         this: *ThisLinker,
         file_path: Fs.Path,
@@ -104,20 +118,15 @@ pub const Linker = struct {
                 return hashed_result.value_ptr.*;
             }
         }
-        var file: std.fs.File = if (fd) |_fd| std.fs.File{ .handle = _fd } else try std.fs.openFileAbsolute(file_path.text, .{ .read = true });
-        Fs.FileSystem.setMaxFd(file.handle);
-        var modkey = try Fs.FileSystem.RealFS.ModKey.generate(&this.fs.fs, file_path.text, file);
-        const hash_name = try modkey.hashName(file_path.name.base);
+
+        const modkey = try this.getModKey(file_path, fd);
+        const hash_name = modkey.hashName(file_path.text);
 
         if (Bundler.isCacheEnabled) {
             var hashed = std.hash.Wyhash.hash(0, file_path.text);
             try this.hashed_filenames.put(hashed, try this.allocator.dupe(u8, hash_name));
         }
 
-        if (this.fs.fs.needToCloseFiles() and fd == null) {
-            file.close();
-        }
-
         return hash_name;
     }
 
@@ -651,6 +660,21 @@ pub const Linker = struct {
 
                     if (use_hashed_name) {
                         var basepath = Fs.Path.init(source_path);
+
+                        if (linker.options.serve) {
+                            var hash_buf: [64]u8 = undefined;
+                            const modkey = try linker.getModKey(basepath, null);
+
+                            return Fs.Path.init(try origin.joinAlloc(
+                                linker.allocator,
+                                std.fmt.bufPrint(&hash_buf, "hash:{x}/", .{modkey.hash()}) catch unreachable,
+                                dirname,
+                                basename,
+                                absolute_pathname.ext,
+                                source_path,
+                            ));
+                        }
+
                         basename = try linker.getHashedFilename(basepath, null);
                     }
 
@@ -690,7 +714,7 @@ pub const Linker = struct {
         import_record.path = try linker.generateImportPath(
             source_dir,
             if (path.is_symlink and import_path_format == .absolute_url and linker.options.platform.isNotBun()) path.pretty else path.text,
-            Bundler.isCacheEnabled and loader == .file,
+            loader == .file,
             path.namespace,
             origin,
             import_path_format,