Add chapters 4, 5, 7

.gitignore

@@ -0,0 +1 @@
+.vscode/

chapter-04/database.sql

@@ -0,0 +1,19 @@
+CREATE DATABASE IF NOT EXISTS chapter04;
+
+USE chapter04;
+
+CREATE TABLE IF NOT EXISTS chapter04.people (
+    name        VARCHAR(100),
+    title       VARCHAR(10),
+    description VARCHAR(100),
+    PRIMARY KEY (name)
+);
+
+DELETE FROM chapter04.people;
+
+INSERT INTO chapter04.people VALUES ('Gru', 'Felonius', 'Where are the minions?');
+INSERT INTO chapter04.people VALUES ('Nefario', 'Dr.', 'Why ... why are you so old?');
+INSERT INTO chapter04.people VALUES ('Agnes', '', 'Your unicorn is so fluffy!');
+INSERT INTO chapter04.people VALUES ('Edith', '', "Don't touch anything!");
+INSERT INTO chapter04.people VALUES ('Vector', '', 'Committing crimes with both direction and magnitude!');
+INSERT INTO chapter04.people VALUES ('Dave', 'Minion', 'Ngaaahaaa! Patalaki patalaku Big Boss!!');

chapter-04/go/.gitignore

@@ -0,0 +1 @@
+vendor/

chapter-04/go/Gopkg.toml

@@ -0,0 +1,11 @@
+[[constraint]]
+  name = "github.com/uber/jaeger-client-go"
+  version = "^2.14.0"
+
+[[constraint]]
+  name = "github.com/go-sql-driver/mysql"
+  version = "1.4.0"
+
+[[constraint]]
+  name = "github.com/opentracing-contrib/go-stdlib"
+  branch = "master"

chapter-04/go/exercise1/hello.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"log"
+	"net/http"
+	"strings"
+
+	"github.com/PacktPublishing/Distributed-Tracing/chapter-04/go/exercise1/people"
+)
+
+var repo *people.Repository
+
+func main() {
+	repo = people.NewRepository()
+	defer repo.Close()
+
+	http.HandleFunc("/sayHello/", handleSayHello)
+
+	log.Print("Listening on http://localhost:8080/")
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}
+
+func handleSayHello(w http.ResponseWriter, r *http.Request) {
+	name := strings.TrimPrefix(r.URL.Path, "/sayHello/")
+	greeting, err := SayHello(name)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Write([]byte(greeting))
+}
+
+// SayHello creates a greeting for the named person.
+func SayHello(name string) (string, error) {
+	person, err := repo.GetPerson(name)
+	if err != nil {
+		return "", err
+	}
+	return FormatGreeting(
+		person.Name,
+		person.Title,
+		person.Description,
+	), nil
+}
+
+// FormatGreeting combines information about a person into a greeting string.
+func FormatGreeting(name, title, description string) string {
+	response := "Hello, "
+	if title != "" {
+		response += title + " "
+	}
+	response += name + "!"
+	if description != "" {
+		response += " " + description
+	}
+	return response
+}

chapter-04/go/exercise1/people/repository.go

@@ -0,0 +1,65 @@
+package people
+
+import (
+	"database/sql"
+	"log"
+
+	_ "github.com/go-sql-driver/mysql"
+
+	"github.com/PacktPublishing/Distributed-Tracing/chapter-04/go/lib/model"
+)
+
+const dburl = "root:mysqlpwd@tcp(127.0.0.1:3306)/chapter04"
+
+// Repository retrieves information about people.
+type Repository struct {
+	db *sql.DB
+}
+
+// NewRepository creates a new Repository backed by MySQL database.
+func NewRepository() *Repository {
+	db, err := sql.Open("mysql", dburl)
+	if err != nil {
+		log.Fatal(err)
+	}
+	err = db.Ping()
+	if err != nil {
+		log.Fatalf("Cannot ping the db: %v", err)
+	}
+	return &Repository{
+		db: db,
+	}
+}
+
+// GetPerson tries to find the person in the database by name.
+// If not found, it still returns a Person object with only name
+// field populated.
+func (r *Repository) GetPerson(name string) (model.Person, error) {
+	query := "select title, description from people where name = ?"
+	rows, err := r.db.Query(query, name)
+	if err != nil {
+		return model.Person{}, err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var title, descr string
+		err := rows.Scan(&title, &descr)
+		if err != nil {
+			return model.Person{}, err
+		}
+		return model.Person{
+			Name:        name,
+			Title:       title,
+			Description: descr,
+		}, nil
+	}
+	return model.Person{
+		Name: name,
+	}, nil
+}
+
+// Close calls close on the underlying db connection.
+func (r *Repository) Close() {
+	r.db.Close()
+}

chapter-04/go/exercise2/hello.go

@@ -0,0 +1,80 @@
+package main
+
+import (
+	"log"
+	"net/http"
+	"strings"
+
+	opentracing "github.com/opentracing/opentracing-go"
+	otlog "github.com/opentracing/opentracing-go/log"
+
+	"github.com/PacktPublishing/Distributed-Tracing/chapter-04/go/exercise2/people"
+	"github.com/PacktPublishing/Distributed-Tracing/chapter-04/go/lib/tracing"
+)
+
+var repo *people.Repository
+var tracer opentracing.Tracer
+
+func main() {
+	repo = people.NewRepository()
+	defer repo.Close()
+
+	tr, closer := tracing.Init("go-2-hello")
+	defer closer.Close()
+	tracer = tr
+
+	http.HandleFunc("/sayHello/", handleSayHello)
+
+	log.Print("Listening on http://localhost:8080/")
+	log.Fatal(http.ListenAndServe(":8080", nil))
+}
+
+func handleSayHello(w http.ResponseWriter, r *http.Request) {
+	span := tracer.StartSpan("say-hello")
+	defer span.Finish()
+
+	name := strings.TrimPrefix(r.URL.Path, "/sayHello/")
+	greeting, err := SayHello(name, span)
+	if err != nil {
+		span.SetTag("error", true)
+		span.LogFields(otlog.Error(err))
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	span.SetTag("response", greeting)
+	w.Write([]byte(greeting))
+}
+
+// SayHello creates a greeting for the named person.
+func SayHello(name string, span opentracing.Span) (string, error) {
+	person, err := repo.GetPerson(name)
+	if err != nil {
+		return "", err
+	}
+
+	span.LogKV(
+		"name", person.Name,
+		"title", person.Title,
+		"description", person.Description,
+	)
+
+	return FormatGreeting(
+		person.Name,
+		person.Title,
+		person.Description,
+	), nil
+}
+
+// FormatGreeting combines information about a person into a greeting string.
+func FormatGreeting(name, title, description string) string {
+	response := "Hello, "
+	if title != "" {
+		response += title + " "
+	}
+	response += name + "!"
+	if description != "" {
+		response += " " + description
+	}
+	return response
+}