read(input, message, options) {
        this.prepare();
        const oneofsHandled = [];
        for (const [jsonKey, jsonValue] of Object.entries(input)) {
            const field = this.fMap[jsonKey];
            if (!field) {
                if (!options.ignoreUnknownFields)
                    throw new Error(`Found unknown field while reading ${this.info.typeName} from JSON format. JSON key: ${jsonKey}`);
                continue;
            }
            const localName = field.localName;
            // handle oneof ADT
            let target; // this will be the target for the field value, whether it is member of a oneof or not
            if (field.oneof) {
                if (jsonValue === null && (field.kind !== 'enum' || field.T()[0] !== 'google.protobuf.NullValue')) {
                    continue;
                }
                // since json objects are unordered by specification, it is not possible to take the last of multiple oneofs
                if (oneofsHandled.includes(field.oneof))
                    throw new Error(`Multiple members of the oneof group "${field.oneof}" of ${this.info.typeName} are present in JSON.`);
                oneofsHandled.push(field.oneof);
                target = message[field.oneof] = {
                    oneofKind: localName
                };
            }
            else {
                target = message;
            }
            // we have handled oneof above. we just have read the value into `target`.
            if (field.kind == 'map') {
                if (jsonValue === null) {
                    continue;
                }
                // check input
                this.assert(json_typings_1.isJsonObject(jsonValue), field.name, jsonValue);
                // our target to put map entries into
                const fieldObj = target[localName];
                // read entries
                for (const [jsonObjKey, jsonObjValue] of Object.entries(jsonValue)) {
                    this.assert(jsonObjValue !== null, field.name + " map value", null);
                    // read value
                    let val;
                    switch (field.V.kind) {
                        case "message":
                            val = field.V.T().internalJsonRead(jsonObjValue, options);
                            break;
                        case "enum":
                            val = this.enum(field.V.T(), jsonObjValue, field.name, options.ignoreUnknownFields);
                            if (val === false)
                                continue;
                            break;
                        case "scalar":
                            val = this.scalar(jsonObjValue, field.V.T, field.V.L, field.name);
                            break;
                    }
                    this.assert(val !== undefined, field.name + " map value", jsonObjValue);
                    // read key
                    let key = jsonObjKey;
                    if (field.K == reflection_info_1.ScalarType.BOOL)
                        key = key == "true" ? true : key == "false" ? false : key;
                    key = this.scalar(key, field.K, reflection_info_1.LongType.STRING, field.name).toString();
                    fieldObj[key] = val;
                }
            }
            else if (field.repeat) {
                if (jsonValue === null)
                    continue;
                // check input
                this.assert(Array.isArray(jsonValue), field.name, jsonValue);
                // our target to put array entries into
                const fieldArr = target[localName];
                // read array entries
                for (const jsonItem of jsonValue) {
                    this.assert(jsonItem !== null, field.name, null);
                    let val;
                    switch (field.kind) {
                        case "message":
                            val = field.T().internalJsonRead(jsonItem, options);
                            break;
                        case "enum":
                            val = this.enum(field.T(), jsonItem, field.name, options.ignoreUnknownFields);
                            if (val === false)
                                continue;
                            break;
                        case "scalar":
                            val = this.scalar(jsonItem, field.T, field.L, field.name);
                            break;
                    }
                    this.assert(val !== undefined, field.name, jsonValue);
                    fieldArr.push(val);
                }
            }
            else {
                switch (field.kind) {
                    case "message":
                        if (jsonValue === null && field.T().typeName != 'google.protobuf.Value') {
                            this.assert(field.oneof === undefined, field.name + " (oneof member)", null);
                            continue;
                        }
                        target[localName] = field.T().internalJsonRead(jsonValue, options, target[localName]);
                        break;
                    case "enum":
                        if (jsonValue === null)
                            continue;
                        let val = this.enum(field.T(), jsonValue, field.name, options.ignoreUnknownFields);
                        if (val === false)
                            continue;
                        target[localName] = val;
                        break;
                    case "scalar":
                        if (jsonValue === null)
                            continue;
                        target[localName] = this.scalar(jsonValue, field.T, field.L, field.name);
                        break;
                }
            }
        }
    }
Reads a message from canonical JSON format into the target message.

Repeated fields are appended. Map entries are added, overwriting
existing keys.

If a message field is already present, it will be merged with the
new data.