Expand docstrings for MsgOption functions and methods.

This commit enhances the docstrings for the MsgOption functions and related methods in msg.go, providing extensive explanations, parameters, and references. It helps users understand the functionality, usage, and context of each function, improving code readability and usability.

msg.go

@@ -150,8 +150,22 @@ const SendmailPath = "/usr/sbin/sendmail"
 // MsgOption is a function type that modifies a Msg instance during its creation or initialization.
 type MsgOption func(*Msg)
 
-// NewMsg creates a new email message with optional MsgOption functions that customize various aspects of the
+// NewMsg creates a new email message with optional MsgOption functions that customize various aspects
-// message.
+// of the message.
+//
+// This function initializes a new Msg instance with default values for address headers, character set,
+// encoding, general headers, and MIME version. It then applies any provided MsgOption functions to
+// customize the message according to the user's needs. If an option is nil, it will be ignored.
+// After applying the options, the function sets the appropriate MIME WordEncoder for the message.
+//
+// Parameters:
+//   - opts: A variadic list of MsgOption functions that can be used to customize the Msg instance.
+//
+// Returns:
+//   - A pointer to the newly created Msg instance.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5321
 func NewMsg(opts ...MsgOption) *Msg {
 	msg := &Msg{
 		addrHeader:    make(map[AddrHeader][]*mail.Address),
@@ -177,64 +191,140 @@ func NewMsg(opts ...MsgOption) *Msg {
 }
 
 // WithCharset sets the Charset type for a Msg during its creation or initialization.
-func WithCharset(c Charset) MsgOption {
+//
+// This MsgOption function allows you to specify the character set to be used in the email message.
+// The charset defines how the text in the message is encoded and interpreted by the email client.
+// This option should be called when creating a new Msg instance to ensure that the desired charset
+// is set correctly.
+//
+// Parameters:
+//   - charset: The Charset value that specifies the desired character set for the Msg.
+//
+// Returns:
+//   - A MsgOption function that can be used to customize the Msg instance.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc2047#section-5
+func WithCharset(charset Charset) MsgOption {
 	return func(m *Msg) {
-		m.charset = c
+		m.charset = charset
 	}
 }
 
 // WithEncoding sets the Encoding type for a Msg during its creation or initialization.
-func WithEncoding(e Encoding) MsgOption {
+//
+// This MsgOption function allows you to specify the encoding type to be used in the email message.
+// The encoding defines how the message content is encoded, which affects how it is transmitted
+// and decoded by email clients. This option should be called when creating a new Msg instance to
+// ensure that the desired encoding is set correctly.
+//
+// Parameters:
+//   - encoding: The Encoding value that specifies the desired encoding type for the Msg.
+//
+// Returns:
+//   - A MsgOption function that can be used to customize the Msg instance.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc2047#section-6
+func WithEncoding(encoding Encoding) MsgOption {
 	return func(m *Msg) {
-		m.encoding = e
+		m.encoding = encoding
 	}
 }
 
 // WithMIMEVersion sets the MIMEVersion type for a Msg during its creation or initialization.
 //
-// Note that in the context of email, MIME Version 1.0 is the only officially standardized and supported
+// Note that in the context of email, MIME Version 1.0 is the only officially standardized and
-// version. While MIME has been updated and extended over time (via various RFCs), these updates and extensions
+// supported version. While MIME has been updated and extended over time via various RFCs, these
-// do not introduce new MIME versions; they refine or add features within the framework of MIME 1.0.
+// updates and extensions do not introduce new MIME versions; they refine or add features within
-// Therefore there should be no reason to ever use this MsgOption.
+// the framework of MIME 1.0. Therefore, there should be no reason to ever use this MsgOption.
-// https://datatracker.ietf.org/doc/html/rfc1521
 //
-// https://datatracker.ietf.org/doc/html/rfc2045
+// Parameters:
+//   - version: The MIMEVersion value that specifies the desired MIME version for the Msg.
 //
-// https://datatracker.ietf.org/doc/html/rfc2049
+// Returns:
-func WithMIMEVersion(mv MIMEVersion) MsgOption {
+//   - A MsgOption function that can be used to customize the Msg instance.
-	return func(m *Msg) {
-		m.mimever = mv
-	}
-}
-
-// WithBoundary sets the boundary of a Msg to the provided string value during its creation or initialization.
 //
-// Note that by default we create random MIME boundaries. This should only be used if a specific boundary is
+// References:
-// required.
+//   - https://datatracker.ietf.org/doc/html/rfc1521
-func WithBoundary(b string) MsgOption {
+//   - https://datatracker.ietf.org/doc/html/rfc2045
+//   - https://datatracker.ietf.org/doc/html/rfc2049
+func WithMIMEVersion(version MIMEVersion) MsgOption {
 	return func(m *Msg) {
-		m.boundary = b
+		m.mimever = version
 	}
 }
 
-// WithMiddleware adds the given Middleware to the end of the list of the Client middlewares slice. Middleware
+// WithBoundary sets the boundary of a Msg to the provided string value during its creation or
-// are processed in FIFO order.
-func WithMiddleware(mw Middleware) MsgOption {
-	return func(m *Msg) {
-		m.middlewares = append(m.middlewares, mw)
-	}
-}
-
-// WithPGPType sets the PGP type for the Msg during its creation or initialization, determining the encryption or
-// signature method.
-func WithPGPType(pt PGPType) MsgOption {
-	return func(m *Msg) {
-		m.pgptype = pt
-	}
-}
-
-// WithNoDefaultUserAgent disables the inclusion of a default User-Agent header in the Msg during its creation or
 // initialization.
+//
+// Note that by default, random MIME boundaries are created. This option should only be used if
+// a specific boundary is required for the email message. Using a predefined boundary can be
+// helpful when constructing multipart messages with specific formatting or content separation.
+//
+// Parameters:
+//   - boundary: The string value that specifies the desired boundary for the Msg.
+//
+// Returns:
+//   - A MsgOption function that can be used to customize the Msg instance.
+func WithBoundary(boundary string) MsgOption {
+	return func(m *Msg) {
+		m.boundary = boundary
+	}
+}
+
+// WithMiddleware adds the given Middleware to the end of the list of the Client middlewares slice.
+// Middleware are processed in FIFO order.
+//
+// This MsgOption function allows you to specify custom middleware that will be applied during the
+// message handling process. Middleware can be used to modify the message, perform logging, or
+// implement additional functionality as the message flows through the system. Each middleware
+// is executed in the order it was added.
+//
+// Parameters:
+//   - middleware: The Middleware to be added to the list for processing.
+//
+// Returns:
+//   - A MsgOption function that can be used to customize the Msg instance.
+func WithMiddleware(middleware Middleware) MsgOption {
+	return func(m *Msg) {
+		m.middlewares = append(m.middlewares, middleware)
+	}
+}
+
+// WithPGPType sets the PGP type for the Msg during its creation or initialization, determining
+// the encryption or signature method.
+//
+// This MsgOption function allows you to specify the PGP (Pretty Good Privacy) type to be used
+// for securing the message. The chosen PGP type influences how the message is encrypted or
+// signed, ensuring confidentiality and integrity of the content. This option should be called
+// when creating a new Msg instance to set the desired PGP type appropriately.
+//
+// Parameters:
+//   - pgptype: The PGPType value that specifies the desired PGP type for the Msg.
+//
+// Returns:
+//   - A MsgOption function that can be used to customize the Msg instance.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc4880
+func WithPGPType(pgptype PGPType) MsgOption {
+	return func(m *Msg) {
+		m.pgptype = pgptype
+	}
+}
+
+// WithNoDefaultUserAgent disables the inclusion of a default User-Agent header in the Msg during
+// its creation or initialization.
+//
+// This MsgOption function allows you to customize the Msg instance by omitting the default
+// User-Agent header, which is typically included to provide information about the software
+// sending the email. This option can be useful when you want to have more control over the
+// headers included in the message, such as when sending from a custom application or for
+// privacy reasons.
+//
+// Returns:
+//   - A MsgOption function that can be used to customize the Msg instance.
 func WithNoDefaultUserAgent() MsgOption {
 	return func(m *Msg) {
 		m.noDefaultUserAgent = true
@@ -242,67 +332,150 @@ func WithNoDefaultUserAgent() MsgOption {
 }
 
 // SetCharset sets or overrides the currently set encoding charset of the Msg.
-func (m *Msg) SetCharset(c Charset) {
+//
-	m.charset = c
+// This method allows you to specify a character set for the email message. The charset is
+// important for ensuring that the content of the message is correctly interpreted by
+// mail clients. Common charset values include UTF-8, ISO-8859-1, and others. If a charset
+// is not explicitly set, CharsetUTF8 is used as default.
+//
+// Parameters:
+//   - charset: The Charset value to set for the Msg, determining the encoding used for the message content.
+func (m *Msg) SetCharset(charset Charset) {
+	m.charset = charset
 }
 
 // SetEncoding sets or overrides the currently set Encoding of the Msg.
-func (m *Msg) SetEncoding(e Encoding) {
+//
-	m.encoding = e
+// This method allows you to specify the encoding type for the email message. The encoding
+// determines how the message content is represented and can affect the size and compatibility
+// of the email. Common encoding types include Base64 and Quoted-Printable. Setting a new
+// encoding may also adjust how the message content is processed and transmitted.
+//
+// Parameters:
+//   - encoding: The Encoding value to set for the Msg, determining the method used to encode the
+//     message content.
+func (m *Msg) SetEncoding(encoding Encoding) {
+	m.encoding = encoding
 	m.setEncoder()
 }
 
 // SetBoundary sets or overrides the currently set boundary of the Msg.
 //
-// Note that by default we create random MIME boundaries. This should only be used if a specific boundary is
+// This method allows you to specify a custom boundary string for the MIME message. The
-// required.
+// boundary is used to separate different parts of the message, especially when dealing
-func (m *Msg) SetBoundary(b string) {
+// with multipart messages. By default, the Msg generates random MIME boundaries. This
-	m.boundary = b
+// function should only be used if you have a specific boundary requirement for the
+// message. Ensure that the boundary value does not conflict with any content within the
+// message to avoid parsing errors.
+//
+// Parameters:
+//   - boundary: The string value representing the boundary to set for the Msg, used in
+//     multipart messages to delimit different sections.
+func (m *Msg) SetBoundary(boundary string) {
+	m.boundary = boundary
 }
 
 // SetMIMEVersion sets or overrides the currently set MIME version of the Msg.
 //
-// Note that in the context of email, MIME Version 1.0 is the only officially standardized and supported
+// In the context of email, MIME Version 1.0 is the only officially standardized and
-// version. While MIME has been updated and extended over time (via various RFCs), these updates and extensions
+// supported version. Although MIME has been updated and extended over time through
-// do not introduce new MIME versions; they refine or add features within the framework of MIME 1.0.
+// various RFCs, these updates do not introduce new MIME versions; they refine or add
-// Therefore there should be no reason to ever use this MsgOption.
+// features within the framework of MIME 1.0. Therefore, there is generally no need to
+// use this function to set a different MIME version.
 //
-// https://datatracker.ietf.org/doc/html/rfc1521
+// Parameters:
+//   - version: The MIMEVersion value to set for the Msg, which determines the MIME
+//     version used in the email message.
 //
-// https://datatracker.ietf.org/doc/html/rfc2045
+// References:
-//
+//   - https://datatracker.ietf.org/doc/html/rfc1521
-// https://datatracker.ietf.org/doc/html/rfc2049
+//   - https://datatracker.ietf.org/doc/html/rfc2045
-func (m *Msg) SetMIMEVersion(mv MIMEVersion) {
+//   - https://datatracker.ietf.org/doc/html/rfc2049
-	m.mimever = mv
+func (m *Msg) SetMIMEVersion(version MIMEVersion) {
+	m.mimever = version
 }
 
-// SetPGPType sets or overrides the currently set PGP type for the Msg, determining the encryption or
+// SetPGPType sets or overrides the currently set PGP type for the Msg, determining the
-// signature method.
+// encryption or signature method.
-func (m *Msg) SetPGPType(t PGPType) {
+//
-	m.pgptype = t
+// This method allows you to specify the PGP type that will be used when encrypting or
+// signing the message. Different PGP types correspond to various encryption and signing
+// algorithms, and selecting the appropriate type is essential for ensuring the security
+// and integrity of the message content.
+//
+// Parameters:
+//   - pgptype: The PGPType value to set for the Msg, which determines the encryption
+//     or signature method used for the email message.
+func (m *Msg) SetPGPType(pgptype PGPType) {
+	m.pgptype = pgptype
 }
 
-// Encoding returns the currently set Encoding of the Msg as string.
+// Encoding returns the currently set Encoding of the Msg as a string.
+//
+// This method retrieves the encoding type that is currently applied to the message. The
+// encoding type determines how the message content is encoded for transmission. Common
+// encoding types include quoted-printable and base64, and the returned string will reflect
+// the specific encoding method in use.
+//
+// Returns:
+//   - A string representation of the current Encoding of the Msg.
 func (m *Msg) Encoding() string {
 	return m.encoding.String()
 }
 
-// Charset returns the currently set Charset of the Msg as string.
+// Charset returns the currently set Charset of the Msg as a string.
+//
+// This method retrieves the character set that is currently applied to the message. The
+// charset defines the encoding for the text content of the message, ensuring that
+// characters are displayed correctly across different email clients and platforms. The
+// returned string will reflect the specific charset in use, such as UTF-8 or ISO-8859-1.
+//
+// Returns:
+//   - A string representation of the current Charset of the Msg.
 func (m *Msg) Charset() string {
 	return m.charset.String()
 }
 
 // SetHeader sets a generic header field of the Msg.
 //
-// Deprecated: This method only exists for compatibility reason. Please use SetGenHeader instead.
+// Deprecated: This method only exists for compatibility reasons. Please use SetGenHeader
-// For adding address headers like "To:" or "From", use SetAddrHeader instead.
+// instead. For adding address headers like "To:" or "From", use SetAddrHeader instead.
+//
+// This method allows you to set a header field for the message, providing the header name
+// and its corresponding values. However, it is recommended to utilize the newer methods
+// for better clarity and functionality. Using SetGenHeader or SetAddrHeader is preferred
+// for more specific header types, ensuring proper handling of the message headers.
+//
+// Parameters:
+//   - header: The header field to set in the Msg.
+//   - values: One or more string values to associate with the header field.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3
+//   - https://datatracker.ietf.org/doc/html/rfc2047
 func (m *Msg) SetHeader(header Header, values ...string) {
 	m.SetGenHeader(header, values...)
 }
 
 // SetGenHeader sets a generic header field of the Msg to the provided list of values.
 //
-// Note: for adding email address related headers (like "To:" or "From") use SetAddrHeader instead.
+// This method is intended for setting generic headers in the email message. It takes a
+// header name and a variadic list of string values, encoding them as necessary before
+// storing them in the message's internal header map.
+//
+// Note: For adding email address-related headers (like "To:", "From", "Cc", etc.),
+// use SetAddrHeader instead to ensure proper formatting and validation.
+//
+// Parameters:
+//   - header: The header field to set in the Msg.
+//   - values: One or more string values to associate with the header field.
+//
+// This method ensures that all values are appropriately encoded for email transmission,
+// adhering to the necessary standards.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3
+//   - https://datatracker.ietf.org/doc/html/rfc2047
 func (m *Msg) SetGenHeader(header Header, values ...string) {
 	if m.genHeader == nil {
 		m.genHeader = make(map[Header][]string)
@@ -315,22 +488,36 @@ func (m *Msg) SetGenHeader(header Header, values ...string) {
 
 // SetHeaderPreformatted sets a generic header field of the Msg, which content is already preformatted.
 //
-// Deprecated: This method only exists for compatibility reason. Please use SetGenHeaderPreformatted instead.
+// Deprecated: This method only exists for compatibility reasons. Please use
+// SetGenHeaderPreformatted instead for setting preformatted generic header fields.
+//
+// Parameters:
+//   - header: The header field to set in the Msg.
+//   - value: The preformatted string value to associate with the header field.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3
+//   - https://datatracker.ietf.org/doc/html/rfc2047
 func (m *Msg) SetHeaderPreformatted(header Header, value string) {
 	m.SetGenHeaderPreformatted(header, value)
 }
 
-// SetGenHeaderPreformatted sets a generic header field of the Msg which content is already preformated.
+// SetGenHeaderPreformatted sets a generic header field of the Msg which content is already preformatted.
 //
 // This method does not take a slice of values but only a single value. The reason for this is that we do not
-// perform any content alteration on these kind of headers and expect the user to have already taken care of
+// perform any content alteration on these kinds of headers and expect the user to have already taken care of
 // any kind of formatting required for the header.
 //
-// Note: This method should be used only as a last resort. Since the user is respondible for the formatting of
+// Note: This method should be used only as a last resort. Since the user is responsible for the formatting of
-// the message header, we cannot guarantee any compliance with the RFC 2822. It is advised to use SetGenHeader
+// the message header, we cannot guarantee any compliance with RFC 2822. It is advised to use SetGenHeader
-// instead.
+// instead for general header fields.
 //
-// https://datatracker.ietf.org/doc/html/rfc2822
+// Parameters:
+//   - header: The header field to set in the Msg.
+//   - value: The preformatted string value to associate with the header field.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc2822
 func (m *Msg) SetGenHeaderPreformatted(header Header, value string) {
 	if m.preformHeader == nil {
 		m.preformHeader = make(map[Header]string)
@@ -340,11 +527,21 @@ func (m *Msg) SetGenHeaderPreformatted(header Header, value string) {
 
 // SetAddrHeader sets the specified AddrHeader for the Msg to the given values.
 //
-// Addresses are parsed according to RFC 5322. If parsing of ANY of the provided values fails,
+// Addresses are parsed according to RFC 5322. If parsing any of the provided values fails,
-// and error is returned. If you cannot guarantee that all provided values are valid, you can
+// an error is returned. If you cannot guarantee that all provided values are valid, you can
-// use SetAddrHeaderIgnoreInvalid instead, which will skip any parsing error silently.
+// use SetAddrHeaderIgnoreInvalid instead, which will silently skip any parsing errors.
 //
-// https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
+// This method allows you to set address-related headers for the message, ensuring that the
+// provided addresses are properly formatted and parsed. Using this method helps maintain the
+// integrity of the email addresses within the message.
+//
+// Parameters:
+//   - header: The AddrHeader to set in the Msg (e.g., "From", "To", "Cc", "Bcc").
+//   - values: One or more string values representing the email addresses to associate with
+//     the specified header.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
 func (m *Msg) SetAddrHeader(header AddrHeader, values ...string) error {
 	if m.addrHeader == nil {
 		m.addrHeader = make(map[AddrHeader][]*mail.Address)
@@ -370,10 +567,19 @@ func (m *Msg) SetAddrHeader(header AddrHeader, values ...string) error {
 
 // SetAddrHeaderIgnoreInvalid sets the specified AddrHeader for the Msg to the given values.
 //
-// Addresses are parsed according to RFC 5322. If parsing of ANY of the provided values fails,
+// Addresses are parsed according to RFC 5322. If parsing of any of the provided values fails,
-// the error is ignored and the address omiitted from the address list.
+// the error is ignored and the address is omitted from the address list.
 //
-// https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
+// This method allows for setting address headers while ignoring invalid addresses. It is useful
+// in scenarios where you want to ensure that only valid addresses are included without halting
+// execution due to parsing errors.
+//
+// Parameters:
+//   - header: The AddrHeader field to set in the Msg.
+//   - values: One or more string values representing email addresses.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
 func (m *Msg) SetAddrHeaderIgnoreInvalid(header AddrHeader, values ...string) {
 	var addresses []*mail.Address
 	for _, addrVal := range values {
@@ -388,36 +594,51 @@ func (m *Msg) SetAddrHeaderIgnoreInvalid(header AddrHeader, values ...string) {
 
 // EnvelopeFrom sets the envelope from address for the Msg.
 //
-// The HeaderEnvelopeFrom address is generally not included in the mail body but only used by the Client for the
+// The HeaderEnvelopeFrom address is generally not included in the mail body but only used by the
-// communication with the SMTP server. If the Msg has no "FROM" address set in the mail body, the msgWriter will
+// Client for communication with the SMTP server. If the Msg has no "FROM" address set in the
-// try to use the envelope from address, if this has been set for the Msg. The provided address is validated
+// mail body, the msgWriter will try to use the envelope from address if it has been set for the Msg.
-// according to RFC 5322 and will return an error if the validation fails.
+// The provided address is validated according to RFC 5322 and will return an error if the validation fails.
 //
-// https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
+// Parameters:
+//   - from: The envelope from address to set in the Msg.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
 func (m *Msg) EnvelopeFrom(from string) error {
 	return m.SetAddrHeader(HeaderEnvelopeFrom, from)
 }
 
 // EnvelopeFromFormat sets the provided name and mail address as HeaderEnvelopeFrom for the Msg.
 //
-// The HeaderEnvelopeFrom address is generally not included in the mail body but only used by the Client for the
+// The HeaderEnvelopeFrom address is generally not included in the mail body but only used by the
-// communication with the SMTP server. If the Msg has no "FROM" address set in the mail body, the msgWriter will
+// Client for communication with the SMTP server. If the Msg has no "FROM" address set in the mail
-// try to use the envelope from address, if this has been set for the Msg. The provided name and address adre
+// body, the msgWriter will try to use the envelope from address if it has been set for the Msg.
-// validated according to RFC 5322 and will return an error if the validation fails.
+// The provided name and address are validated according to RFC 5322 and will return an error if
+// the validation fails.
 //
-// https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
+// Parameters:
+//   - name: The name to associate with the envelope from address.
+//   - addr: The mail address to set as the envelope from address.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3.4
 func (m *Msg) EnvelopeFromFormat(name, addr string) error {
 	return m.SetAddrHeader(HeaderEnvelopeFrom, fmt.Sprintf(`"%s" <%s>`, name, addr))
 }
 
 // From sets the "FROM" address in the mail body for the Msg.
 //
-// The "FROM" address is included in the mail body and indicates the sender of the message to the recipient.
+// The "FROM" address is included in the mail body and indicates the sender of the message to
-// This address is visible in the email client and is typically displayed to the recipient. If the "FROM" address
+// the recipient. This address is visible in the email client and is typically displayed to the
-// is not set, the msgWriter may attempt to use the envelope from address (if available) for sending. The provided
+// recipient. If the "FROM" address is not set, the msgWriter may attempt to use the envelope
-// address is validated according to RFC 5322 and will return an error if the validation fails.
+// from address (if available) for sending. The provided address is validated according to RFC
+// 5322 and will return an error if the validation fails.
 //
-// https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.2
+// Parameters:
+//   - from: The "FROM" address to set in the mail body.
+//
+// References:
+//   - https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.2
 func (m *Msg) From(from string) error {
 	return m.SetAddrHeader(HeaderFrom, from)
 }