Musicians are often guarded, but PnB Rock is not one you need to press for answers.

Deep into rehearsals for his sold-out hometown show at The Met Philadelphia on Friday, the Germantown native tackles difficult topics with a bluntness of the Philly persuasion. Rock, 27, has stayed forthcoming for a lofty purpose: He hopes his improbable infiltration of mainstream hip-hop will light a fire under the next him.

“I’m an open book. I want everybody to know that I ain’t hiding nothing,” says the difficult-to-label melody maker, whose sophomore album, TrapStar Turnt PopStar, is expected out on Atlantic Records in 2019. “Young kids see me, hear my story, and they know how I came up. They see what I’m doing now and think, ‘Damn, this is achievable.’ ”

That story begins at the corner of Pastorius and Baynton Streets, the intersection that provided Rock and his associates with the “PnB” honorific preceding each of their recording monikers. Born Rakim Hasheem Allen, Rock was one of five boys raised by a single mother, Hanunah, “a real music head” who exposed her son to a diverse discography — classic rap (yes, he’s named after that Rakim), rock-and-roll, Motown, Philly soul. “I was interested in music because she was into it,” he says.

His mother, in turn, recognized that her son was born with natural musical ability, talent she pushed him to cultivate. “She had tried to put me in singing classes, because she thought I had a nice voice,” recalls Rock, who resisted the encouragement. “I never thought music would be my calling. I was still stuck on being in the streets.”

Rock’s run-ins with the law are rooted in his early teens. Both his biological dad and his uncle, who served as a father figure, were killed when he was very young, setting his struggling family on an unpredictable trajectory — “place to place, house to house, shelter to shelter.” Instability in his home life led to serious conflicts with other students. “I was a problem child, as far as my attitude and my behavior,” he says. “I’m wavy, but my clothes are dirty, so people are joking on me.”

Expelled from Germantown High, Rock rattled between disciplinary programs, juvenile detention, and alternative schools before dropping out. (“I definitely regret not graduating,” he says.) He was kicked out of his house, crashing with friends, squatting in model homes, and running the streets full-time. At 19, he was sentenced to 33 months in state prison for drug-related crimes.

Rock looks backs on this period at SCI Forest in Marienville, Pa. as the most pivotal time in his creative development. “In the penitentiary, you have music all around you,” he says. “People are making beats on keyboards and rapping in circles all day. I was part of that. I’d go into my cell and write music on my own time.”

With no hip-hop radio available in remote Forest County, Rock found himself constantly “listening to Top 40 music.” Prolonged exposure to artists like Drake, Katy Perry and Rihanna inspired him to infuse his distinctive songwriting style, informed by the freewheeling delivery and hook-heavy structure of ’90s R & B, with an accessible pop sensibility. Positive feedback from fellow inmates convinced him that “this is the sound people like — so I should stick with it.”

Hunkered down in the indelible territory between rapper and crooner and armed with intricate, conversational melodies and cocksure yet introspective songwriting, Rock reveals his roguish charisma over contemporary trap production. He cuts his confessional exploration of sex, love, and relationships with deeply topical and personal storytelling, exemplified by early singles like “My City Needs Something,” a heart-wrenching indictment of the violence that defined his upbringing (“Good die young, ain’t how it’s supposed to be / Every time I turn around / I lose somebody close to me”).

Much of the music Rock crafted on the inside made it onto 2015’s RNB 1, the first in a series of grassroots, self-released mixtapes that got him on Atlantic’s radar. “I generated a big buzz. … The music I was putting out, it was believable, there was a story behind it,” says Rock, who leaned on social media to cultivate an engaged local, and eventually national, following.

Released in early 2017, mixtape GTTM: Going Thru the Motions hit the Top 10 on Billboard’s US Top R & B/Hip-Hop charts, largely on the strength of “Selfish,” a sentimental swoon of a single that’s his biggest hit to date. That same year saw his proper major-label debut, Catch These Vibes; as well as a high-profile feature alongside Kodak Black and A Boogie wit da Hoodie on “Horses,” off The Fate of the Furious soundtrack.

TrapStar Turnt PopStar will be a double album, its title hinting at the stylistic split in play between the two discs — the first chronicling “how I got to where I’m at,” while the second celebrates “the pop side of me: the new PnB, the swag, the drip.” The dualistic perspective is something Rock plans to explore in theatrical fashion at Friday’s concert, the first hip-hop show to be booked at the newly renovated 3,500-seat Met. “I’m gonna treat it like it’s my first show — a kid on the first day of school. My outfit’s already laid out,” says Rock, who still lives in Philadelphia when he’s not on the road recording or performing.

As his clout expands, Rock is sure to emphasize that he and his career are maturing in real time — and he vows to remain transparent. The birth of his daughter Milan, now 5, has changed his perspective, helping to strengthen his once-rocky relationship with his mother, too. Still, “I ain’t this perfect person,” he says. “I’m still growing. My whole aura, my whole attitude is because I came from the trap. There definitely wouldn’t be no new me without the old me. I had to go through all of that to be this.”

MUSIC

PnB Rock

8 p.m. Friday, The Met Philadelphia, 858 N. Broad St., Sold out, 800-745-3000, themetphilly.com