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Common tags #549
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122 changes: 122 additions & 0 deletions
122
components/proxy/src/main/kotlin/com/hotels/styx/CommonTags.kt
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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| Copyright (C) 2013-2019 Expedia Inc. | ||
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| 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 | ||
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| http://www.apache.org/licenses/LICENSE-2.0 | ||
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| 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. | ||
| */ | ||
| package com.hotels.styx | ||
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| /** | ||
| * A common tag representation. | ||
| * | ||
| * Enforces a common tag format and provides a set of higher order functionality | ||
| * that operate on provided `name`, `encode` and `decode` properties. | ||
| * | ||
| * A tag string is a name-value pair separated by equal ('=') sign: | ||
| * | ||
| * tag-string = name "=" value-part | ||
| * | ||
| * `encode` and `decode` are functions to encode a T to a value-part string, | ||
| * and to decode the value-part string back to T. | ||
| * | ||
| * @property name a tag name | ||
| * @property encode a function that encodes a value of T as a tag value string | ||
| * @property decode a function that decodes a tag value string as a T | ||
| */ | ||
| sealed class CommonValueTag<T>( | ||
| val name: String, | ||
| val encode: (T) -> String?, | ||
| val decode: (String) -> T?) { | ||
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| /** | ||
| * Extracts value part (the right hand side) from a tag string. | ||
| * | ||
| * @param tag a tag string | ||
| * @return the tag value | ||
| */ | ||
| fun valuePart(tag: String) = if (tag.startsWith("$name=")) { | ||
| tag.removePrefix("$name=") | ||
| } else { | ||
| null | ||
| } | ||
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| /** | ||
| * Tests if a given string matches this tag. A match is positive when the string | ||
| * starts with `name` followed by `=`. | ||
| * | ||
| * @param a tag string | ||
| * @return True if this string is possibly a matching tag. Otherwise return false. | ||
| */ | ||
| fun match(tag: String) = tag.startsWith("$name=") | ||
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| /** | ||
| * Decodes given tag string to its typed value. | ||
| * | ||
| * @param tag a tag string | ||
| * @return a decoded tag value, or null if decoding failed | ||
| */ | ||
| fun valueOf(tag: String) = valuePart(tag) | ||
| ?.let { decode(it) } | ||
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| /** | ||
| * Find this tag from a set of tag strings. If found, decode the tag value. Return null if | ||
| * tag was not found, or if decoding failed. | ||
| * | ||
| * @param tags a set of tag strings | ||
| * @return A decoded value if tag was found. Otherwise return null. | ||
| */ | ||
| fun find(tags: Set<String>) = tags.firstOrNull { this.match(it) } | ||
| ?.let { valuePart(it) } | ||
| ?.let { this.decode(it) } | ||
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| /** | ||
| * Removes all instances of this tag from a set of tag strings. | ||
| * Return a new Set<String> with all instances of this tag removed. | ||
| * | ||
| * @param tags a set of tag strings | ||
| * @return A new set of strings without this tag. | ||
| */ | ||
| fun remove(tags: Set<String>) = tags | ||
| .filterNot { this.match(it) } | ||
| .toSet() | ||
| } | ||
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| /** | ||
| * A NullableValueTag invoke method returns null when value cannot be encoded to string. | ||
| * The API consumer must handle this situation. | ||
| */ | ||
| class NullableValueTag<T>( | ||
| name: String, | ||
| encode: (T) -> String?, | ||
| decode: (String) -> T?) : CommonValueTag<T>(name, encode, decode) { | ||
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| operator fun invoke(value: T): String? = encode(value) | ||
| ?.let { | ||
| "$name=$it" | ||
| } | ||
| } | ||
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| /** | ||
| * A SafeValueTag invoke method throws a KotlinNullPointerException when the | ||
| * tag value cannot be encoded to string. | ||
| */ | ||
| class SafeValueTag<T>( | ||
| name: String, | ||
| encode: (T) -> String?, | ||
| decode: (String) -> T?) : CommonValueTag<T>(name, encode, decode) { | ||
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| operator fun invoke(value: T): String = encode(value) | ||
| .let { | ||
| it!! | ||
| "$name=$it" | ||
| } | ||
| } | ||
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Is it worth providing defaults for encode and decode as
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Is this possible without knowing the type T?