create-spdx: Get SPDX-License-Identifier from source

This patch will read the begining of source files and try to find
the SPDX-License-Identifier to populate the licenseInfoInFiles
field for each source file. This does not populate licenseConcluded
at this time, nor rolls it up to package level.

We read as binary file since some source code seem to have some
binary characters, the license is then converted to ascii strings.

(From OE-Core rev: 51e5f328635eb022143178c3169bae719509697a)

Signed-off-by: Saul Wold <saul.wold@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/create-spdx.bbclass

@@ -37,6 +37,23 @@ SPDX_SUPPLIER[doc] = "The SPDX PackageSupplier field for SPDX packages created f
 
 do_image_complete[depends] = "virtual/kernel:do_create_spdx"
 
+def extract_licenses(filename):
+    import re
+
+    lic_regex = re.compile(b'^\W*SPDX-License-Identifier:\s*([ \w\d.()+-]+?)(?:\s+\W*)?$', re.MULTILINE)
+
+    try:
+        with open(filename, 'rb') as f:
+            size = min(15000, os.stat(filename).st_size)
+            txt = f.read(size)
+            licenses = re.findall(lic_regex, txt)
+            if licenses:
+                ascii_licenses = [lic.decode('ascii') for lic in licenses]
+                return ascii_licenses
+    except Exception as e:
+        bb.warn(f"Exception reading {filename}: {e}")
+    return None
+
 def get_doc_namespace(d, doc):
     import uuid
     namespace_uuid = uuid.uuid5(uuid.NAMESPACE_DNS, d.getVar("SPDX_UUID_NAMESPACE"))
@@ -232,6 +249,11 @@ def add_package_files(d, doc, spdx_pkg, topdir, get_spdxid, get_types, *, archiv
                         checksumValue=bb.utils.sha256_file(filepath),
                     ))
 
+                if "SOURCE" in spdx_file.fileTypes:
+                    extracted_lics = extract_licenses(filepath)
+                    if extracted_lics:
+                        spdx_file.licenseInfoInFiles = extracted_lics
+
                 doc.files.append(spdx_file)
                 doc.add_relationship(spdx_pkg, "CONTAINS", spdx_file)
                 spdx_pkg.hasFiles.append(spdx_file.SPDXID)