Introduced functional method to extract certificate model from the gr… (

#6)

* Introduced functional method to extract certificate model from the green certificate QR

decoder/src/main/java/dgca/verifier/app/decoder/CertificateDecoder.kt

@@ -0,0 +1,57 @@
+/*
+ *  ---license-start
+ *  eu-digital-green-certificates / dgca-verifier-app-android
+ *  ---
+ *  Copyright (C) 2021 T-Systems International GmbH and all other contributors
+ *  ---
+ *  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.
+ *  ---license-end
+ *
+ *  Created by osarapulov on 5/10/21 11:28 PM
+ */
+
+package dgca.verifier.app.decoder
+
+import dgca.verifier.app.decoder.model.GreenCertificate
+
+/**
+ * Represents error that might occur during decoding green certificate QR.
+ */
+sealed class CertificateDecodingError(val error: Throwable? = null) {
+    class Base45DecodingError(error: Throwable) : CertificateDecodingError(error)
+    class Base45DecompressionError(error: Throwable) : CertificateDecodingError(error)
+    class CoseDataDecodingError(error: Throwable) : CertificateDecodingError(error)
+    class GreenCertificateDecodingError(error: Throwable) : CertificateDecodingError(error)
+    object EmptyGreenCertificate : CertificateDecodingError()
+    class CertificateConversionError(error: Throwable) : CertificateDecodingError(error)
+}
+
+/**
+ * Represents green certificate decoding result. If it's successful - it should return {@link Success},
+ * specific descriptive error {@link Error}.
+ */
+sealed class CertificateDecodingResult {
+    class Success(val greenCertificate: GreenCertificate) : CertificateDecodingResult()
+    data class Error(val error: CertificateDecodingError) : CertificateDecodingResult()
+}
+
+/**
+ * Provides ability to decode QR code representing green certificate to local model {@link CertificateModel}
+ */
+interface CertificateDecoder {
+
+    /**
+     * Returns success result with {@link CertificateModel} or descriptive error model.
+     */
+    fun decodeCertificate(qrCodeText: String): CertificateDecodingResult
+}

decoder/src/main/java/dgca/verifier/app/decoder/DefaultCertificateDecoder.kt

@@ -0,0 +1,110 @@
+/*
+ *  ---license-start
+ *  eu-digital-green-certificates / dgca-verifier-app-android
+ *  ---
+ *  Copyright (C) 2021 T-Systems International GmbH and all other contributors
+ *  ---
+ *  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.
+ *  ---license-end
+ *
+ *  Created by osarapulov on 5/10/21 11:29 PM
+ */
+
+package dgca.verifier.app.decoder
+
+import COSE.HeaderKeys
+import com.fasterxml.jackson.dataformat.cbor.databind.CBORMapper
+import com.upokecenter.cbor.CBORObject
+import dgca.verifier.app.decoder.base45.Base45Decoder
+import dgca.verifier.app.decoder.cwt.CwtHeaderKeys
+import dgca.verifier.app.decoder.model.CoseData
+import dgca.verifier.app.decoder.model.GreenCertificate
+import java.time.Instant
+import java.util.zip.InflaterInputStream
+
+@ExperimentalUnsignedTypes
+class DefaultCertificateDecoder(private val base45Decoder: Base45Decoder) :
+    CertificateDecoder {
+    companion object {
+        const val PREFIX = "HC1:"
+    }
+
+    override fun decodeCertificate(qrCodeText: String): CertificateDecodingResult {
+        val withoutPrefix: String = if (qrCodeText.startsWith(PREFIX)) qrCodeText.drop(PREFIX.length) else qrCodeText
+        val base45Decoded: ByteArray = try {
+            base45Decoder.decode(withoutPrefix)
+        } catch (error: Throwable) {
+            return CertificateDecodingResult.Error(CertificateDecodingError.Base45DecodingError(error))
+        }
+
+        val decompressed: ByteArray = try {
+            base45Decoded.decompressBase45DecodedData()
+        } catch (error: Throwable) {
+            return CertificateDecodingResult.Error(CertificateDecodingError.Base45DecompressionError(error))
+        }
+
+        val coseData: CoseData = try {
+            decompressed.decodeCose()
+        } catch (error: Throwable) {
+            return CertificateDecodingResult.Error(CertificateDecodingError.CoseDataDecodingError(error))
+        }
+
+        val greenCertificate: GreenCertificate = try {
+            coseData.cbor.decodeGreenCertificate()
+        } catch (error: Throwable) {
+            return CertificateDecodingResult.Error(CertificateDecodingError.GreenCertificateDecodingError(error))
+        } ?: return CertificateDecodingResult.Error(CertificateDecodingError.EmptyGreenCertificate)
+
+
+        return CertificateDecodingResult.Success(greenCertificate)
+    }
+
+
+    private fun ByteArray.decompressBase45DecodedData(): ByteArray {
+        // ZLIB magic headers
+        return if (this.size >= 2 && this[0] == 0x78.toByte() && (
+                    this[1] == 0x01.toByte() || // Level 1
+                            this[1] == 0x5E.toByte() || // Level 2 - 5
+                            this[1] == 0x9C.toByte() || // Level 6
+                            this[1] == 0xDA.toByte()
+                    )
+        ) {
+            InflaterInputStream(this.inputStream()).readBytes()
+        } else this
+    }
+
+    private fun ByteArray.decodeCose(): CoseData {
+        val messageObject = CBORObject.DecodeFromBytes(this)
+        val content = messageObject[2].GetByteString()
+        val rgbProtected = messageObject[0].GetByteString()
+        val key = HeaderKeys.KID.AsCBOR()
+        val objProtected = CBORObject.DecodeFromBytes(rgbProtected).get(key).GetByteString()
+        return CoseData(content, objProtected)
+    }
+
+    private fun ByteArray.decodeGreenCertificate(): GreenCertificate? {
+        val map = CBORObject.DecodeFromBytes(this)
+
+        val issuedAt = Instant.ofEpochSecond(map[CwtHeaderKeys.ISSUED_AT.asCBOR()].AsInt64())
+        if (issuedAt.isAfter(Instant.now())) throw IllegalArgumentException("IssuedAt not correct: $issuedAt")
+
+        val expirationTime = Instant.ofEpochSecond(map[CwtHeaderKeys.EXPIRATION.asCBOR()].AsInt64())
+        if (expirationTime.isBefore(Instant.now())) throw IllegalArgumentException("Expiration not correct: $expirationTime")
+
+        val hcert = map[CwtHeaderKeys.HCERT.asCBOR()]
+        val hcertv1 = hcert[CBORObject.FromObject(1)].EncodeToBytes()
+
+        return CBORMapper()
+            .readValue(hcertv1, GreenCertificate::class.java)
+    }
+}