teach json parsing about map patterns

src/aws.zig

@@ -485,6 +485,42 @@ test "basic json request serialization" {
         \\}
     , buffer.items);
 }
+test "layer object only" {
+    const TestResponse = struct {
+        arn: ?[]const u8 = null,
+        // uncompressed_code_size: ?i64 = null,
+
+        pub fn jsonFieldNameFor(_: @This(), comptime field_name: []const u8) []const u8 {
+            const mappings = .{
+                .arn = "Arn",
+            };
+            return @field(mappings, field_name);
+        }
+    };
+    const response =
+        \\        {
+        \\          "UncompressedCodeSize": 2,
+        \\          "Arn": "blah"
+        \\        }
+    ;
+    // const response =
+    //     \\        {
+    //     \\          "UncompressedCodeSize": 22599541,
+    //     \\          "Arn": "arn:aws:lambda:us-west-2:550620852718:layer:PollyNotes-lib:4"
+    //     \\        }
+    // ;
+    const allocator = std.testing.allocator;
+    var stream = json.TokenStream.init(response);
+    const parser_options = json.ParseOptions{
+        .allocator = allocator,
+        .allow_camel_case_conversion = true, // new option
+        .allow_snake_case_conversion = true, // new option
+        .allow_unknown_fields = true, // new option. Cannot yet handle non-struct fields though
+        .allow_missing_fields = false, // new option. Cannot yet handle non-struct fields though
+    };
+    const r = try json.parse(TestResponse, &stream, parser_options);
+    json.parseFree(TestResponse, r, parser_options);
+}
 // Use for debugging json responses of specific requests
 // test "dummy request" {
 //     const allocator = std.testing.allocator;

src/json.zig

@@ -1136,6 +1136,9 @@ pub const TokenStream = struct {
             return error.UnexpectedEndOfJson;
         }
     }
+    fn stackUsed(self: *TokenStream) u8 {
+        return self.parser.stack_used + if (self.token != null) @as(u8, 1) else 0;
+    }
 };
 
 fn checkNext(p: *TokenStream, id: std.meta.Tag(Token)) !void {
@@ -1532,6 +1535,20 @@ fn snakeCaseComp(field: []const u8, key: []const u8, options: ParseOptions) !boo
 
     return std.mem.eql(u8, comp_field, normalized_key);
 }
+const SkipValueError = error{UnexpectedJsonDepth} || TokenStream.Error;
+
+fn skipValue(tokens: *TokenStream) SkipValueError!void {
+    const original_depth = tokens.stackUsed();
+
+    // Return an error if no value is found
+    _ = try tokens.next();
+    if (tokens.stackUsed() < original_depth) return error.UnexpectedJsonDepth;
+    if (tokens.stackUsed() == original_depth) return;
+
+    while (try tokens.next()) |_| {
+        if (tokens.stackUsed() == original_depth) return;
+    }
+}
 
 fn parseInternal(comptime T: type, token: Token, tokens: *TokenStream, options: ParseOptions) !T {
     switch (@typeInfo(T)) {
@@ -1675,6 +1692,7 @@ fn parseInternal(comptime T: type, token: Token, tokens: *TokenStream, options:
                             }
                         }
                         if (!found and !options.allow_unknown_fields) return error.UnknownField;
+                        if (!found) try skipValue(tokens);
                     },
                     .ObjectBegin => {
                         if (!options.allow_unknown_fields) return error.UnknownField;
@@ -1788,6 +1806,35 @@ fn parseInternal(comptime T: type, token: Token, tokens: *TokenStream, options:
                                 },
                             }
                         },
+                        .ObjectBegin => {
+                            // We are parsing into a slice, but we have an
+                            // ObjectBegin. This might be ok, iff the type
+                            // follows this pattern: []struct { key: []const u8, value: anytype }
+                            // (could key be anytype?).
+                            if (!isMapPattern(T))
+                                return error.UnexpectedToken;
+                            var arraylist = std.ArrayList(ptrInfo.child).init(allocator);
+                            errdefer {
+                                while (arraylist.popOrNull()) |v| {
+                                    parseFree(ptrInfo.child, v, options);
+                                }
+                                arraylist.deinit();
+                            }
+                            while (true) {
+                                const key = (try tokens.next()) orelse return error.UnexpectedEndOfJson;
+                                switch (key) {
+                                    .ObjectEnd => break,
+                                    else => {},
+                                }
+
+                                try arraylist.ensureCapacity(arraylist.items.len + 1);
+                                const key_val = try parseInternal(try typeForField(ptrInfo.child, "key"), key, tokens, options);
+                                const val = (try tokens.next()) orelse return error.UnexpectedEndOfJson;
+                                const val_val = try parseInternal(try typeForField(ptrInfo.child, "value"), val, tokens, options);
+                                arraylist.appendAssumeCapacity(.{ .key = key_val, .value = val_val });
+                            }
+                            return arraylist.toOwnedSlice();
+                        },
                         else => return error.UnexpectedToken,
                     }
                 },
@@ -1799,6 +1846,40 @@ fn parseInternal(comptime T: type, token: Token, tokens: *TokenStream, options:
     unreachable;
 }
 
+fn typeForField(comptime T: type, field_name: []const u8) !type {
+    const ti = @typeInfo(T);
+    switch (ti) {
+        .Struct => {
+            inline for (ti.Struct.fields) |field| {
+                if (std.mem.eql(u8, field.name, field_name))
+                    return field.field_type;
+            }
+        },
+        else => return error.TypeIsNotAStruct, // should not hit this
+    }
+    return error.FieldNotFound;
+}
+
+fn isMapPattern(comptime T: type) bool {
+    // We should be getting a type that is a pointer to a slice.
+    // Let's just double check before proceeding
+    const ti = @typeInfo(T);
+    if (ti != .Pointer) return false;
+    if (ti.Pointer.size != .Slice) return false;
+    const ti_child = @typeInfo(ti.Pointer.child);
+    if (ti_child != .Struct) return false;
+    if (ti_child.Struct.fields.len != 2) return false;
+    var key_found = false;
+    var value_found = false;
+    inline for (ti_child.Struct.fields) |field| {
+        if (std.mem.eql(u8, "key", field.name))
+            key_found = true;
+        if (std.mem.eql(u8, "value", field.name))
+            value_found = true;
+    }
+    return key_found and value_found;
+}
+
 pub fn parse(comptime T: type, tokens: *TokenStream, options: ParseOptions) !T {
     const token = (try tokens.next()) orelse return error.UnexpectedEndOfJson;
     return parseInternal(T, token, tokens, options);
@@ -1904,6 +1985,15 @@ test "parse into that allocates a slice" {
     }
 }
 
+test "parse into that uses a map pattern" {
+    const options = ParseOptions{ .allocator = testing.allocator };
+    const Map = []struct { key: []const u8, value: []const u8 };
+    const r = try parse(Map, &TokenStream.init("{\"foo\": \"bar\"}"), options);
+    defer parseFree(Map, r, options);
+    try testing.expectEqualSlices(u8, "foo", r[0].key);
+    try testing.expectEqualSlices(u8, "bar", r[0].value);
+}
+
 test "parse into tagged union" {
     {
         const T = union(enum) {