Added example for licensediff

Signed-off-by: Steve Winslow <swinslow@gmail.com>

2 files changed, 117 insertions, 0 deletions

diff --git a/examples/6-licensediff/example_licensediff.go b/examples/6-licensediff/example_licensediff.go
new file mode 100644
index 0000000..d7ff562
--- /dev/null
+++ b/examples/6-licensediff/example_licensediff.go
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+
+// Example for: *licensediff*, *tvloader*
+
+// This example demonstrates loading two SPDX tag-value files from disk into
+// memory, and generating a diff of the concluded licenses for Files in the
+// first-listed Packages in each document.
+// This is generally only useful when run with two SPDX documents that
+// describe licenses for subsequent versions of the same set of files.
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/swinslow/spdx-go/v0/licensediff"
+	"github.com/swinslow/spdx-go/v0/tvloader"
+)
+
+func main() {
+
+	// check that we've received the right number of arguments
+	args := os.Args
+	if len(args) != 3 {
+		fmt.Printf("Usage: %v <spdx-file-first> <spdx-file-second>\n", args[0])
+		fmt.Printf("  Load SPDX 2.1 tag-value files <spdx-file-first> and <spdx-file-second>,\n")
+		fmt.Printf("  run a diff between their concluded licenses, and print basic results.\n")
+		return
+	}
+
+	// open the first SPDX file
+	filenameFirst := args[1]
+	r, err := os.Open(filenameFirst)
+	if err != nil {
+		fmt.Printf("Error while opening %v for reading: %v", filenameFirst, err)
+		return
+	}
+	defer r.Close()
+
+	// try to load the first SPDX file's contents as a tag-value file, version 2.1
+	docFirst, err := tvloader.Load2_1(r)
+	if err != nil {
+		fmt.Printf("Error while parsing %v: %v", filenameFirst, err)
+		return
+	}
+	// make sure it has at least one Package
+	if len(docFirst.Packages) < 1 {
+		fmt.Printf("Error, no packages found in SPDX file %s\n", filenameFirst)
+		return
+	}
+
+	// if we got here, the file is now loaded into memory.
+	fmt.Printf("Successfully loaded first SPDX file %s\n", filenameFirst)
+
+	// open the second SPDX file
+	filenameSecond := args[2]
+	r, err = os.Open(filenameSecond)
+	if err != nil {
+		fmt.Printf("Error while opening %v for reading: %v", filenameSecond, err)
+		return
+	}
+	defer r.Close()
+
+	// try to load the second SPDX file's contents as a tag-value file, version 2.1
+	docSecond, err := tvloader.Load2_1(r)
+	if err != nil {
+		fmt.Printf("Error while parsing %v: %v", filenameSecond, err)
+		return
+	}
+	// make sure it has at least one Package
+	if len(docSecond.Packages) < 1 {
+		fmt.Printf("Error, no packages found in SPDX file %s\n", filenameSecond)
+		return
+	}
+
+	// if we got here, the file is now loaded into memory.
+	fmt.Printf("Successfully loaded second SPDX file %s\n\n", filenameSecond)
+
+	// extract the first-listed package from each Document.
+	// (there could be more than one Package within a Document. For
+	// purposes of this example, we'll just look at the first one.)
+	// we've already confirmed above that each has at least one Package.
+	p1 := docFirst.Packages[0]
+	p2 := docSecond.Packages[0]
+
+	// now, run a diff between the two
+	pairs, err := licensediff.MakePairs(p1, p2)
+	if err != nil {
+		fmt.Printf("Error generating licensediff pairs: %v\n", err)
+		return
+	}
+
+	// take the pairs and turn them into a more structured results set
+	resultSet, err := licensediff.MakeResults(pairs)
+	if err != nil {
+		fmt.Printf("Error generating licensediff results set: %v\n", err)
+		return
+	}
+
+	// print some information about the results
+	fmt.Printf("Files in first only: %d\n", len(resultSet.InFirstOnly))
+	fmt.Printf("Files in second only: %d\n", len(resultSet.InSecondOnly))
+	fmt.Printf("Files in both with different licenses: %d\n", len(resultSet.InBothChanged))
+	fmt.Printf("Files in both with same licenses: %d\n", len(resultSet.InBothSame))
+}
diff --git a/examples/README.md b/examples/README.md
index 64e41f2..19a58b9 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -42,3 +42,14 @@ Package and File license fields; and saving the resulting document to disk.
 This example demonstrates loading an SPDX tag-value file from disk into memory,
 generating a basic report listing counts of the concluded licenses for its
 files, and printing the report to standard output.
+
+## 6-licensediff
+
+*licensediff*, *tvloader*
+
+This example demonstrates loading two SPDX tag-value files from disk into
+memory, and generating a diff of the concluded licenses for Files in the
+first-listed Packages in each document.
+
+This is generally only useful when run with two SPDX documents that describe
+licenses for subsequent versions of the same set of files.