change get api deal with the 500 code

src/main/kotlin/io/ipfs/kotlin/commands/Get.kt

@@ -1,6 +1,8 @@
 package io.ipfs.kotlin.commands
 
-import io.ipfs.kotlin.IPFSConnection
+import com.le.ipfsapi.IPFSConnection
+import okhttp3.Request
+import okhttp3.Response
 import okhttp3.ResponseBody
 import java.io.InputStream
 
@@ -11,25 +13,58 @@ class Get(val ipfs: IPFSConnection) {
      *
      * @param hash The hash of the content in base58.
      */
-    fun cat(hash: String): String = ipfs.callCmd("cat/$hash").use(ResponseBody::string)
+    fun cat(hash: String): String? {
+        val response = catApi(hash)
+        return if (response.isSuccessful && null != response.body()) {
+            response.body()!!.use(ResponseBody::string)
+        } else {
+            null
+        }
+    }
 
     /**
      * Cat IPFS content and return it as ByteArray.
      *
      * @param hash The hash of the content in base58.
      */
-    fun catBytes(hash: String): ByteArray = ipfs.callCmd("cat/$hash").use(ResponseBody::bytes)
+    fun catBytes(hash: String): ByteArray? {
+        val response = catApi(hash)
+        return if (response.isSuccessful && null != response.body()) {
+            response.body()!!.use { it.bytes() }
+        } else {
+            null
+        }
+    }
 
     /**
      * Cat IPFS content and process it using InputStream.
      *
      * @param hash The hash of the content in base58.
      * @param handler Callback which handle processing the input stream. When the callback return the stream and the request body will be closed.
      */
-    fun catStream(hash: String, handler: (stream: InputStream) -> Unit): Unit =
-            ipfs.callCmd("cat/$hash").use { body ->
-                val inputStream = body.byteStream()
-                inputStream.use(handler)
-            }
+    fun catStream(hash: String, handler: (stream: InputStream?) -> Unit): Unit {
+        val response = catApi(hash)
+        if (response.isSuccessful && null != response.body()) {
+            response.body()!!.use { it.byteStream().use(handler) }
+        } else {
+            handler.invoke(null)
+        }
+    }
+
+    /**
+     * If you cat a wrong hash, the ipfs http api will response code 500
+     * and with message. In this case if we use the response boy and cover it
+     * to stream or byte ,it will not the true content of the hash code,it will
+     * be the content of the 'Wrong Message'.
+     *
+     * So we need check the response code by {response.isSuccessful} to insure
+     * we go the right response.
+     */
+    private fun catApi(hash: String):Response{
+        val request = Request.Builder()
+            .url(ipfs.config.base_url + "cat/$hash")
+            .build()
+        return ipfs.config.okHttpClient.newCall(request).execute()
+    }
 
 }