[AI] Structured Output streaming #15652
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| // Copyright 2025 Google LLC | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // http://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
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| import Foundation | ||
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| /// A parser that attempts to parse partial JSON strings into `JSONValue`. | ||
| /// | ||
| /// This parser is tolerant of incomplete JSON structures (e.g., unclosed objects, arrays, strings) | ||
| /// and attempts to return the valid structure parsed so far. This is useful for streaming | ||
| /// applications where JSON is received in chunks. | ||
| @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *) | ||
| final class PartialJSONParser { | ||
| private let input: [Character] | ||
| private var index: Int | ||
| private let length: Int | ||
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| init(input: String) { | ||
| self.input = Array(input) | ||
| index = 0 | ||
| length = self.input.count | ||
| } | ||
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| /// Parses the input string into a `JSONValue`. | ||
| /// Returns `nil` if the input is empty or cannot be parsed as a value. | ||
| func parse() -> JSONValue? { | ||
| skipWhitespace() | ||
| if index >= length { | ||
| return nil | ||
| } | ||
| return parseValue() | ||
| } | ||
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| private func parseValue() -> JSONValue? { | ||
| skipWhitespace() | ||
| if index >= length { return nil } | ||
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| let char = input[index] | ||
| switch char { | ||
| case "{": | ||
| return parseObject() | ||
| case "[": | ||
| return parseArray() | ||
| case "\"": | ||
| return parseString() | ||
| case "t": | ||
| return parseTrue() | ||
| case "f": | ||
| return parseFalse() | ||
| case "n": | ||
| return parseNull() | ||
| case "-", "0" ... "9": | ||
| return parseNumber() | ||
| default: | ||
| // If we encounter an unexpected character, we might be in an invalid state. | ||
| return nil | ||
| } | ||
| } | ||
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| private func parseObject() -> JSONValue { | ||
| // Consume '{' | ||
| index += 1 | ||
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| var object: JSONObject = [:] | ||
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| while index < length { | ||
| skipWhitespace() | ||
| if index >= length { | ||
| // EOF inside object, return what we have | ||
| return .object(object) | ||
| } | ||
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| let char = input[index] | ||
| if char == "}" { | ||
| index += 1 | ||
| return .object(object) | ||
| } | ||
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| // Expect key | ||
| if char == "\"" { | ||
| // Parse key | ||
| // parseString returns .string(val) or .null (actually never .null if called on quote) | ||
| if case let .string(key) = parseString() { | ||
| skipWhitespace() | ||
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| // Expect ':' | ||
| if index < length, input[index] == ":" { | ||
| index += 1 // consume ':' | ||
| if let value = parseValue() { | ||
| object[key] = value | ||
| } | ||
| // If value is nil (EOF), we ignore this key | ||
| } | ||
| } | ||
| } else { | ||
| // Unexpected character in object, maybe a comma? | ||
| if char == "," { | ||
| index += 1 | ||
| continue | ||
| } | ||
| // Invalid or unexpected, abort and return what we have | ||
| return .object(object) | ||
| } | ||
| } | ||
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| return .object(object) | ||
| } | ||
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| private func parseArray() -> JSONValue { | ||
| // Consume '[' | ||
| index += 1 | ||
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| var array: [JSONValue] = [] | ||
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| while index < length { | ||
| skipWhitespace() | ||
| if index >= length { | ||
| return .array(array) | ||
| } | ||
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| let char = input[index] | ||
| if char == "]" { | ||
| index += 1 | ||
| return .array(array) | ||
| } | ||
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| if char == "," { | ||
| index += 1 | ||
| continue | ||
| } | ||
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| if let value = parseValue() { | ||
| array.append(value) | ||
| } else { | ||
| // EOF or invalid | ||
| return .array(array) | ||
| } | ||
| } | ||
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| return .array(array) | ||
| } | ||
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| private func parseString() -> JSONValue { | ||
| // Consume '"' | ||
| index += 1 | ||
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| var string = "" | ||
| var escaped = false | ||
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| while index < length { | ||
| let char = input[index] | ||
| index += 1 | ||
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| if escaped { | ||
| // Handle basic escapes | ||
| switch char { | ||
| case "\"": string.append("\"") | ||
| case "\\": string.append("\\") | ||
| case "/": string.append("/") | ||
| case "b": string.append("\u{08}") | ||
| case "f": string.append("\u{0C}") | ||
| case "n": string.append("\n") | ||
| case "r": string.append("\r") | ||
| case "t": string.append("\t") | ||
| case "u": | ||
| // Unicode escape | ||
| // Need 4 chars | ||
| if index + 4 <= length { | ||
| let hex = String(input[index ..< index + 4]) | ||
| if let scalar = Int(hex, radix: 16), let uScalar = UnicodeScalar(scalar) { | ||
| string.append(Character(uScalar)) | ||
| index += 4 | ||
| } else { | ||
| // Invalid unicode, just append u... | ||
| string.append("\\u") | ||
| } | ||
| } else { | ||
| // Incomplete unicode | ||
| string.append("\\u") | ||
| // And we are probably near EOF | ||
| } | ||
| default: | ||
| string.append(char) | ||
| } | ||
| escaped = false | ||
| } else { | ||
| if char == "\"" { | ||
| return .string(string) | ||
| } else if char == "\\" { | ||
| escaped = true | ||
| } else { | ||
| string.append(char) | ||
| } | ||
| } | ||
| } | ||
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| // Hit EOF without closing quote | ||
| // Return what we have | ||
| return .string(string) | ||
| } | ||
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| private func parseNumber() -> JSONValue? { | ||
| let start = index | ||
| // Consume until non-numeric | ||
| // allowed: 0-9, -, +, ., e, E | ||
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| while index < length { | ||
| let char = input[index] | ||
| if "0123456789-+.eE".contains(char) { | ||
| index += 1 | ||
| } else { | ||
| break | ||
| } | ||
| } | ||
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| let numberString = String(input[start ..< index]) | ||
| if let double = Double(numberString) { | ||
| return .number(double) | ||
| } | ||
| // If partial number (e.g. "-"), return nil | ||
| return nil | ||
| } | ||
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| private func parseTrue() -> JSONValue? { | ||
| // Expect "true" | ||
| if match("true") { return .bool(true) } | ||
| return nil | ||
| } | ||
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| private func parseFalse() -> JSONValue? { | ||
| if match("false") { return .bool(false) } | ||
| return nil | ||
| } | ||
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| private func parseNull() -> JSONValue? { | ||
| if match("null") { return .null } | ||
| return nil | ||
| } | ||
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| private func match(_ string: String) -> Bool { | ||
| let chars = Array(string) | ||
| if index + chars.count <= length { | ||
| if Array(input[index ..< index + chars.count]) == chars { | ||
| index += chars.count | ||
| return true | ||
| } | ||
| } | ||
| return false | ||
| } | ||
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| private func skipWhitespace() { | ||
| while index < length { | ||
| let char = input[index] | ||
| if char.isWhitespace { | ||
| index += 1 | ||
| } else { | ||
| break | ||
| } | ||
| } | ||
| } | ||
| } | ||
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