将 Flow<Byte> 转换为 Flow<String> 在 Kotlin 中

huangapple
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英文:

Transforming a Flow<Byte> to a Flow<String> in Kotlin

问题

考虑我有一个UTF-8字节的_cold_源（例如：从磁盘上读取文件或HTTP响应的主体），以Flow&lt;Byte&gt;的形式。我如何将上述源转换为字符串的_flow_？

换句话说，我希望以下行为：

  1. /*
  2.  * 一个多行字符串，不以换行字符结尾。
  3.  */
  4. val string = &quot;&quot;&quot;
  5.     first line
  6.     第二行
  7.     третья строка
  8. &quot;&quot;&quot;.trimIndent()
  10. assertNotEquals(&#39;\n&#39;, string.last())
  11. assertEquals(2, string.asSequence().count { it == &#39;\n&#39; })
  13. val source: Flow&lt;Byte&gt; = string.toByteArray().asSequence().asFlow()
  15. val transformed: Flow&lt;String&gt; = TODO()
  17. val target = runBlocking {
  18.     transformed.toList(mutableListOf()).toTypedArray()
  19. }
  21. assertArrayEquals(
  22.     arrayOf(&quot;first line&quot;, &quot;第二行&quot;, &quot;третья строка&quot;),
  23.     target
  24. )

作为额外限制，这是一个Kotlin/JS项目，因此无法使用java.io API。

英文:

Consider I have a cold source of UTF-8 bytes (e. g.: reading a file on disk, or the body of an HTTP response), in a form of a Flow&lt;Byte&gt;. How do I convert the above source to a flow of strings?

In other words, I want the following behaviour:

  1. 		/*
  2. 		 * A multi-line string, not terminated with a newline character.
  3. 		 */
  4. 		val string = &quot;&quot;&quot;
  5. 			first line
  6. 			第二行
  7. 			третья строка
  8. 		&quot;&quot;&quot;.trimIndent()
  10. 		assertNotEquals(&#39;\n&#39;, string.last())
  11. 		assertEquals(2, string.asSequence().count { it == &#39;\n&#39; })
  13. 		val source: Flow&lt;Byte&gt; = string.toByteArray().asSequence().asFlow()
  15. 		val transformed: Flow&lt;String&gt; = TODO()
  17. 		val target = runBlocking {
  18. 			transformed.toList(mutableListOf()).toTypedArray()
  19. 		}
  21. 		assertArrayEquals(
  22. 			arrayOf(&quot;first line&quot;, &quot;第二行&quot;, &quot;третья строка&quot;),
  23. 			target
  24. 		)

As an extra restriction, this is a Kotlin/JS project, so java.io APIs can't be used.

答案1

得分: 1

以下是翻译好的代码部分：

  1. fun Flow<Byte>.decodeToString(): Flow<String> =
  2.     flow {
  3.         val buffer: MutableList<Byte> = arrayListOf()
  5.         collect { value ->
  6.             when (value) {
  7.                 /*
  8.                  * Ignore.
  9.                  */
  10.                 '\r'.code.toByte() -> Unit
  12.                 '\n'.code.toByte() -> {
  13.                     emit(buffer)
  14.                     buffer.clear()
  15.                 }
  17.                 else -> buffer.add(value)
  18.             }
  19.         }
  21.         if (buffer.isNotEmpty()) {
  22.             emit(buffer)
  23.         }
  24.     }
  25.     .map(Collection<Byte>::toByteArray)
  26.     .map(ByteArray::decodeToString)

上面的 ArrayList<Byte> 可以替换为 _okio_ 中的 okio.Buffer 或 _kotlinx-io_ 中的 kotlinx.io.core.BytePacketBuilder，例如：

  1. import kotlinx.coroutines.flow.Flow
  2. import kotlinx.coroutines.flow.flow
  3. import okio.Buffer
  5. fun Flow<Byte>.decodeToString(): Flow<String> =
  6.     flow {
  7.         val buffer = Buffer()
  9.         collect { value ->
  10.             when (value) {
  11.                 /*
  12.                  * Ignore.
  13.                  */
  14.                 '\r'.code.toByte() -> Unit
  16.                 '\n'.code.toByte() -> {
  17.                     emit(buffer.readUtf8())
  18.                     buffer.clear()
  19.                 }
  21.                 else -> buffer.writeByte(value.toInt())
  22.             }
  23.         }
  25.         if (buffer.size > 0) {
  26.             emit(buffer.readUtf8())
  27.         }
  28.     }
英文:

Eventually, I came up with the following solution:

  1. fun Flow&lt;Byte&gt;.decodeToString(): Flow&lt;String&gt; =
  2. 	flow {
  3. 		val buffer: MutableList&lt;Byte&gt; = arrayListOf()
  5. 		collect { value -&gt;
  6. 			when (value) {
  7. 				/*
  8. 				 * Ignore.
  9. 				 */
  10. 				&#39;\r&#39;.code.toByte() -&gt; Unit
  12. 				&#39;\n&#39;.code.toByte() -&gt; {
  13. 					emit(buffer)
  14. 					buffer.clear()
  15. 				}
  17. 				else -&gt; buffer.add(value)
  18. 			}
  19. 		}
  21. 		if (buffer.isNotEmpty()) {
  22. 			emit(buffer)
  23. 		}
  24. 	}
  25. 		.map(Collection&lt;Byte&gt;::toByteArray)
  26. 		.map(ByteArray::decodeToString)

The ArrayList&lt;Byte&gt; above can be replaced with either okio.Buffer from okio or kotlinx.io.core.BytePacketBuilder from kotlinx-io, e.g.:

  1. import kotlinx.coroutines.flow.Flow
  2. import kotlinx.coroutines.flow.flow
  3. import okio.Buffer
  5. fun Flow&lt;Byte&gt;.decodeToString(): Flow&lt;String&gt; =
  6. 	flow {
  7. 		val buffer = Buffer()
  9. 		collect { value -&gt;
  10. 			when (value) {
  11. 				/*
  12. 				 * Ignore.
  13. 				 */
  14. 				&#39;\r&#39;.code.toByte() -&gt; Unit
  16. 				&#39;\n&#39;.code.toByte() -&gt; {
  17. 					emit(buffer.readUtf8())
  18. 					buffer.clear()
  19. 				}
  21. 				else -&gt; buffer.writeByte(value.toInt())
  22. 			}
  23. 		}
  25. 		if (buffer.size &gt; 0) {
  26. 			emit(buffer.readUtf8())
  27. 		}
  28. 	}

huangapple
  • 本文由 发表于 2023年2月8日 17:08:02
  • 转载请务必保留本文链接：https://go.coder-hub.com/75383429.html
  • kotlin
  • kotlin-coroutines
  • kotlin-js
  • kotlin-multiplatform
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